Multiplexed communication in a storage device

ABSTRACT

A method is provided, for example, to implement multiplexed communication on an analog bus between a recording channel and a preamplifier in a storage device. A first input of read data circuitry within the recording channel is switchably connected to a first analog line of the analog bus to receive read data transmitted from the preamplifier to the recording channel over the first analog line during a read operation. In addition, a write data output of write data circuitry within the recording channel is switchably connected to the first analog line of the analog bus to transmit write data from the recording channel to the preamplifier over the first analog line during a write operation.

FIELD OF THE INVENTION

The field generally relates to data storage devices and, in particular,to communication between components of a data storage device.

BACKGROUND

Data storage devices such as hard disk drives are utilized fornon-volatile data storage in a wide variety of data processing systems.In a magnetic disk storage device, a storage disk comprises a substratemade from a non-magnetic material, such as aluminum or glass, which iscoated with one or more thin layers of magnetic material. In operation,data is read from, and written to, tracks of a magnetic storage diskusing a magnetic head that includes a read sensor and write element. Ingeneral, a storage device includes a preamplifier that is configured todrive a read sensor in the magnetic head to read data from a magneticstorage disk and amplify the read data, as well as drive a write elementin the magnetic to write data to the storage disk. Moreover, a storagedevice includes recording channel that is configured to decode read datathat is received from the preamplifier, and encode write data that is tobe written to the storage disk. Communication between the preamplifierand the recording channel is implemented using an analog bus and adigital bus, for example. A conventional analog bus comprises aplurality of analog signal lines, which enable high-speed transmissionof analog read and write data signals between the recording channel andthe preamplifier. Each analog signal line is a dedicated line thattransmits either read data or write data. Further, a conventionaldigital bus implements a three wire serial port comprising a clocksignal line, a data line, and an enable line, which serves to transmitdigital control signals for setup and status monitoring of configurationregisters located within the preamplifier. Other digital controlfunctions that require dedicated digital control lines and which cannottolerate the polling and latency characteristic of the serial port aretransmitted on a bit-significant basis on additional dedicated controlbus lines. These conventional communication schemes are inefficient interms of the number of signal lines that are required to transmit dataand control signals between the recording channel, preamplifier, and acontroller.

SUMMARY

In an embodiment of the invention, a method is provided to implementmultiplexed communication on an analog bus between a recording channeland a preamplifier in a storage device. A first input of read datacircuitry within the recording channel is switchably connected to afirst analog line of the analog bus to receive read data transmittedfrom the preamplifier to the recording channel over the first analogline during a read operation. In addition, a write data output of writedata circuitry within the recording channel is switchably connected tothe first analog line of the analog bus to transmit write data from therecording channel to the preamplifier over the first analog line duringa write operation.

Other embodiments include, without limitation, circuits, systems,integrated circuit devices, storage devices, storage systems, andcomputer-readable media.

DESCRIPTION OF THE FIGURES

FIG. 1 schematically illustrates a storage device according to anembodiment of the invention.

FIG. 2 is a schematic block diagram that illustrates a more detailedembodiment of the storage device of FIG. 1 having circuitry to supportmultiplexed communication in a storage device according to an embodimentof the invention.

FIG. 3 is a schematic block diagram that illustrates a more detailedembodiment of the storage device of FIG. 1 having circuitry to supportmultiplexed communication in a storage device according to anotherembodiment of the invention.

FIG. 4 is a table that comparatively illustrates a number of signallines needed for a non-multiplexed analog bus as compared to a number ofsignal lines used for a multiplexed analog bus according to variousembodiments of the invention.

FIG. 5 is a flow diagram of a method to implement multiplexedcommunication between a controller and a preamplifier in a storagedevice using a digital bus comprising a single bidirectional serial dataline and a single clock signal line, according to an embodiment of theinvention.

FIG. 6 is a timing diagram that illustrates a method to control adirection switch on a bidirectional serial data line of a digital bus,according to an embodiment of the invention.

FIG. 7 is a timing diagram that illustrates a method to control adirection switch on a bidirectional serial data line of a digital bus,according to another embodiment of the invention.

FIG. 8 is a flow diagram of method to align a synchronous clock signalwith digital signals to be transmitted over a bidirectional serial dataline using a skew measurement protocol, according to an embodiment ofthe invention.

FIG. 9 is a block diagram of skew measurement circuitry according to anembodiment of the invention.

FIG. 10 is a timing diagram that illustrates a method of operation ofthe skew measurement circuitry of FIG. 9, according to an embodiment ofthe invention.

FIG. 11 is a diagram of a current mode logic implementation of acommunication link with reset circuitry to force a reset of apreamplifier by temporarily changing a common-mode voltage on abidirectional serial data line or a clock signal line of a digital bus,according to an embodiment of the invention.

FIG. 12 is a block diagram of a virtual storage system incorporating aplurality of disk-based storage devices of the type shown in FIG. 1.

WRITTEN DESCRIPTION

FIG. 1 schematically illustrates a storage device 10 according to anembodiment of the invention. The storage device 10 comprises asystem-on-chip 100 that includes various integrated circuits such as ahard disk controller 102, a host interface controller 104, a motorcontroller 106, a memory controller 108, recording channel circuitry110, synchronous serial port control circuitry 112, and buffer memory114. An internal bus 116 enables communication between the hard diskcontroller 102, the host interface controller 104, the motor controller106, the recording channel circuitry 110, and the synchronous serialport control circuitry 112. The system-on-chip 100 further comprises aplurality of interfaces such as a host interface connector 118, a memoryinterface 120, and a servo interface 122. The storage device 10 furthercomprises preamplifier circuitry 130, an external random access memory140, and a read/write head and disk assembly 150.

The storage device 10 further comprises an analog bus 200 and a digitalbus 202. The analog bus 200 connects the recording channel circuitry 110and the preamplifier circuitry 130. The digital bus 202 connects thesynchronous serial port control circuitry 112 and the preamplifiercircuitry 130. In one embodiment of the invention, the analog bus 200comprises a plurality of analog lines that are controlled bymultiplexing circuitry, wherein the multiplexing circuitry controlsbidirectional transmission of read and write information signals betweenthe recording channel circuitry 110 and the preamplifier circuitry 130over one or more analog lines of the analog bus 200.

Further, in one embodiment of the invention, the digital bus 202comprises a clock signal line and a bidirectional serial data lineconnected between the synchronous serial port control circuitry 112 andthe preamplifier circuitry 130. The bidirectional serial data line ofthe digital bus 202 is controlled by multiplexing circuitry, wherein themultiplexing circuitry controls bidirectional transmission of variousdigital signals between the synchronous serial port control circuitry112 and the preamplifier circuitry 130 over the bidirectional serialdata line. The synchronous serial port control circuitry 112 comprisesmaster port logic circuitry that operates in conjunction with slave portlogic circuitry in the preamplifier circuit 130 to control themultiplexed, bidirectional transfer of digital signals over the digitalbus 202. Moreover, the synchronous serial port control circuitry 112generates a synchronous clock signal that is transmitted on the clocksignal line of the digital bus 202 from the synchronous serial portcontrol circuitry 112 to the preamplifier circuitry 130. The synchronousclock signal serves to synchronize transfer and processing of thedigital signals transmitted on the bidirectional serial data line of thedigital bus 202.

In one embodiment of the invention, the analog bus 200 and digital bus202 are implemented using a flexible cable or flex-cable in which signaltransmission is implemented using differential driver circuitry. Asexplained in further detail below, by using multiplexing circuitry toshare signal lines for transmitting different types of informationsignals over the analog bus 200 and digital bus 202, the number ofindividual signal lines that are used to implement the analog bus 200and digital bus 202 to transmit such signals is minimized. Exampleembodiments of the analog bus 200 and the digital bus 202 and theassociated multiplexing control interface will be explained in furtherdetail below with reference to FIGS. 2 and 3, for example.

In general, the preamplifier circuitry 130 is implemented using aprocess technology that is optimized for transmission and/or processingof analog signals. For example, in one embodiment, the preamplifiercircuitry 130 is implemented using a mixed bipolar and CMOS processingtechnology. The recording channel circuitry 110 is implemented using aprocess technology that is optimized for transmission and/or processingof digital signals. For example, in one embodiment of the invention, therecording channel circuitry 110 is implemented using a CMOS processingtechnology.

The read/write head and disk assembly 150 comprises various componentssuch as a spindle motor 160, a spindle 165, a storage medium 170, amagnetic read/write head 180 (or simply, “magnetic head”) disposed onone end of a positioning arm 185, and an actuator motor 190 (or voicecoil motor) connected to one end of the positioning arm 185 opposite themagnetic head 180. The storage medium 170 has a storage surface coatedwith one or more magnetic materials that are capable of storing databits in the form of respective groups of media grains oriented in acommon magnetization direction (e.g., up or down). The storage medium170 is connected to the spindle 165, and the spindle 165 is driven bythe spindle motor 160 to spin the storage medium 170 at high speed. Datais read from and written to the storage medium 170 via the magnetic head180 mounted on the positioning arm 185. The actuator motor 190 comprisesa permanent magnet and a moving coil motor, which operate tocontrollably swing the magnetic head 180 into a desired position acrossthe magnetic surface of the storage medium 170 as the storage medium 170spins by operation of the spindle motor 160.

In general, a sequence of magnetic flux transitions corresponding to adigital data sequence are written onto the magnetic surface of thestorage medium 170 using the magnetic head 180. The digital datasequence serves to modulate current in the write coil of the magnetichead 180. The magnetic surface of storage medium 170 comprises aplurality of concentric tracks, wherein each track is subdivided into aplurality of sectors that are capable of storing a block of sector datafor subsequent retrieval. Moreover, the storage medium 170 furthercomprises timing patterns formed on the surface thereof, which compriseone or more sets of servo address marks (SAMs) or other types of servomarks formed in particular sectors in a conventional manner

The host interface connector 118 represents a physical connector andassociated input/output (I/O) bus wiring that connects the storagedevice 10 to a host system, device, I/O bus, or other components of adata processing system. The I/O data is moved to and from the storagedevice 10 through the host interface connector 118 under control of thehost interface controller 104. The host interface controller 104implements communication protocols for communicating with a host systemor device and controlling and managing data I/O operations, using one ormore known interface standards. For example, in one or more alternativeembodiments of the invention, the host interface connector 118 and thehost interface controller 104 are implemented using one or more of SmallComputer interface (SCSI), Serial Attached SCSI (SAS), Serial AdvancedTechnology Attachment (SATA) and/or Fibre Channel (FC) interfacestandards, for example.

The hard disk controller 102 controls the overall operations of writingand reading data to and from the storage medium 170. In one embodimentof the invention, the hard disk controller 102 is a programmablemicroprocessor or microcontroller. In other embodiments, the hard diskcontroller 102 may be implemented using other known architectures thatare suitable for controlling hard disk operations. The recording channelcircuitry 110 encodes and decodes data that is written to and read fromthe storage medium 170 using the magnetic head 180. The recordingchannel circuitry 110 comprises various types of circuitry that arecommonly implemented in a recording channel to process data that is readfrom and written to the storage medium 170, the details of which are notnecessary to one of ordinary skill in the art for understandingembodiments of the invention as discussed herein.

The preamplifier circuitry 130 is connected between the recordingchannel circuitry 110 and the magnetic head 180. In one embodiment, thepreamplifier circuitry 130 is disposed proximate to a pivot location ofthe actuator motor 190. Flexible printed-circuit cables are used toconnect the magnetic head 180 to the preamplifier circuitry 130. Thepreamplifier circuitry 130 amplifies an analog signal output from themagnetic head 180 for input to the recording channel circuitry 110 andprovides a bias voltage for driving the read sensors of the magnetichead 180.

The motor controller 106 is connected to the head/disk assembly 150 viathe servo interface 122. The motor controller 106 sends control signalsto the spindle motor 160 and actuator motor 190 through the servointerface 122 during read and write operations to spin the storagemedium 170 and move the magnetic head 180 into a target position. Inparticular, for a typical read operation, read command signals forperforming a read operation are received through the host interfaceconnector 118 and sent to the hard disk controller 102 through the hostinterface controller 104 over the internal bus 116. The hard diskcontroller 102 processes the read command signals for performing theread operation and then sends control signals to the motor controller106 for controlling the actuator motor 190 and spindle motor 160 for theread operation. Additionally, the hard disk controller 102 sends theprocessed read signals to the recording channel circuitry 110, which arethen sent to the actuator motor 190 through the preamplifier circuitry130 to perform the read operation. The actuator motor 190 positions themagnetic head 180 over a target data track on storage medium 170 inresponse to control signals received by the motor controller 106 and therecording channel circuitry 110. The motor controller 106 also generatescontrol signals to drive the spindle motor 160 to spin the storagemedium 170 under the direction of the hard disk controller 102. Thespindle motor 160 spins the storage medium 170 at a determined spinrate.

When the magnetic head 180 is positioned adjacent a target data track,magnetic signals representing data on the storage medium 170 are sensedby magnetic head 180 as the storage medium 170 is rotated by the spindlemotor 160. The sensed magnetic signals are provided as continuous,minute analog signals (read back signals) representative of the magneticdata on the storage medium 170. The analog read back signals aretransferred from the magnetic head 180 to the recording channelcircuitry 110 via the preamplifier circuitry 130. The preamplifiercircuitry 130 amplifies the analog read back signals accessed fromstorage medium 170, and the recording channel circuitry 110 decodes anddigitizes the amplified analog read back signals to recreate theinformation originally written to the storage medium 170. The data readfrom the storage medium 170 is then output to a host system or devicethrough the host interface controller 104 and host interface connector118 under control of the hard disk controller 102.

A write operation is substantially the opposite of a read operation. Forexample, in one embodiment, write data and command signals forperforming write operations are received through the host interfaceconnector 118, wherein the write signals represent commands to perform awrite operation and/or data that is to be written to the storage medium170. The write signals are sent to the hard disk controller 102 throughhost interface controller 104. The hard disk controller 102 processesthe write signals for performing the write operation and then sendscontrol signals to the motor controller 106 for controlling the actuatormotor 190 and spindle motor 160 for the write operation. Additionally,the hard disk controller 102 sends the processed write signals (andformatted data) to the recording channel circuitry 110, wherein theformatted data to be written is encoded. The write signals (control anddata) are then sent to the head/disk assembly 150 via the preamplifiercircuitry 130 to perform a write operation by writing data to thestorage medium 170 via the magnetic head 180.

In the embodiment of FIG. 1, the random access memory 140, the buffermemory 114, the memory controller 108, and the memory bus 120 areconfigured to perform or otherwise support data caching and bufferingfunctions that are typically implemented in data storage devices, aswell as store and enable access to firmware sequences that controloperation of the hard disk controller 102 and other components connectedthereto. The random access memory 140 is an external memory relative tothe system-on-chip 100 and other components of the storage device 10,but is nonetheless internal to the storage device 10. In one embodiment,the external random access memory 140 is a double data rate synchronousdynamic random access memory, although a wide variety of other types ofmemory may be used in alternate embodiments.

It is to be understood that the external random access memory 140,system-on-chip 100 and preamplifier circuitry 130 shown in FIG. 1collectively represent one embodiment of “control circuitry” as thatterm is utilized herein. Numerous alternative embodiments of “controlcircuitry” include a subset of the components 100, 130 and 140 orportions of one or more of these components. For example, thesystem-on-chip 100 itself may be viewed as an example of “controlcircuitry” to process data received from and supplied to the magnetichead 180 and to control positioning of the magnetic head 180 relative tothe storage medium 170. Certain operations of the system-on-chip 100 inthe storage device 10 of FIG. 1 may be directed by the hard diskcontroller 102, which executes code stored in the external random accessmemory 140 and/or the buffer memory 114, for example. Thus, at least aportion of the control functionality of the storage device 10 may beimplemented at least in part in the form of software code.

Furthermore, although the embodiment of FIG. 1 illustrates variouscomponents of the system-on-chip 100 being implemented on a singleintegrated circuit chip, the system-on-chip 100 may include otherintegrated circuits, such as the external random access memory 140 orthe preamplifier circuitry 130, or portions thereof. Moreover, the harddisk controller 102, host interface controller 104, motor controller106, and synchronous serial port control circuitry 112 may beimplemented using suitable integrated circuit architectures such asmicroprocessor, digital signal processor (DSP), application-specificintegrated circuit (ASIC), or field-programmable gate array (FPGA), orother types of integrated circuit architectures.

While FIG. 1 shows an embodiment of the invention with a single instanceof each of the storage medium 170, magnetic head 180, and positioningarm 185, it is to be understood that in an alternate embodiment of theinvention, the storage device 10 comprises multiple instances of one ormore of these or other drive components. For example, in an alternativeembodiment of the invention, the storage device 10 comprises multiplestorage disks attached to the same spindle such that each storage diskrotates at the same speed, as well as multiple magnetic read/write headsand associated positioning arms coupled to one or more actuators.Moreover, it is to be understood that a read/write head as that term isbroadly used herein may be implemented in the form of a combination ofseparate read and write heads. More particularly, the term “read/write”as used herein is intended to be construed broadly as read and/or write,such that a read/write head may comprise one or more read heads only,one or more write heads only, a single head used for both reading andwriting, or a combination of separate read and write heads. Such headsmay comprise, for example, write heads with wrap-around or side-shieldedmain poles, or any other types of heads suitable for recording and/orreading data on a storage disk.

In addition, the storage device 10 as illustrated in FIG. 1 may includeother elements in addition to, or in place of, those specifically shown,including one or more elements of a type commonly found in conventionalstorage devices. These and other conventional elements, being wellunderstood by those skilled in the art, are not described in detailherein. It should also be understood that the particular arrangement ofelements shown in FIG. 1 is presented by way of illustrative exampleonly. Those skilled in the art will recognize that a wide variety ofother storage device configurations may be used in implementingembodiments of the invention.

FIG. 2 is a schematic block diagram that illustrates a more detailedembodiment of the storage device of FIG. 1 having circuitry to supportmultiplexed communication in a storage device according to an embodimentof the invention. More specifically, FIG. 2 illustrates detailedembodiments of the recording channel circuitry 110, the synchronousserial port control circuitry 112, the preamplifier circuitry 130, themagnetic head 180, the analog bus 200, and the digital bus 202, whichare configured to support multiplexed communication in the storagedevice 10 of FIG. 1.

As shown in FIG. 2, the analog bus 200 comprises a plurality of analogsignal lines 200-1, 200-2, and 200-3. In one embodiment of theinvention, as depicted in FIG. 2, the analog signal lines 200-1, 200-2,and 200-3 are implemented as differential signal lines to assure noiseimmunity and signal quality of analog signals (or digital signals) thatare transmitted over the analog bus 200 between the recording channelcircuitry 110 and the preamplifier circuitry 130. In other embodiments,the analog signal lines 200-1, 200-2, and 200-3 are implemented assingle wires, or other types of signal lines that are suitable for thegiven application. The recording channel circuitry 110 and thepreamplifier circuitry 130 comprise multiplexing circuitry 204/206which, as explained in further detail below, is configured to controlmultiplexed transmission of read and write information signals (controland/or data signals) over the plurality of analog lines 200-1, 200-2,and 200-3 of the analog bus 200 between the recording channel circuitry110 and the preamplifier circuitry 130.

Moreover, the digital bus 202 consists of a bidirectional serial dataline 202-1, and a unidirectional clock signal line 202-2, which areconnected between the synchronous serial port control circuitry 112 andthe preamplifier circuitry 130. In one embodiment of the invention, asdepicted in FIG. 2, the bidirectional serial data line 202-1 and theclock signal line 202-2 are implemented as differential signal lines soas to enable the transmission of high-rate data streams that are used totransmit digital signals (control data and commands) over thebidirectional serial data line 202-1, as well as transmit an associatedhigh-frequency synchronous clock signal over the clock signal line202-2. In other embodiments, the digital bus 202 can be implemented withsingle wires, or other types of signal lines that are suitable for thegiven application. The synchronous serial port control circuitry 112 andthe preamplifier circuitry 130 comprise multiplexing circuitry 208/210which, as explained in further detail below, is configured to controlbidirectional, multiplexed transmission of digital signals over thebidirectional serial data line 202-1 of the digital bus 202.

As further shown in FIG. 2, the recording channel circuitry 110comprises read data circuitry 212 and write data circuitry 214. Inaddition, the synchronous serial port control circuitry 112 comprisesport logic circuitry 216, a clock generator 218, alignment circuitry220, and a driver 222. Moreover, the preamplifier circuitry 130comprises port logic circuitry 226, a gap detector circuit 228, phasedetector circuitry 230, fly height control circuitry 232, read circuitry234, 236 and 238, write circuitry 240, pattern dependent write circuitryand/or heat assisted magnetic recording circuitry 242, bit-patternedmagnetic recording loopback circuitry 244, and register bank and commandlogic circuitry 246. The magnetic head 180 comprises a spacing sensor180-1, a heater element 180-2, a plurality of read sensors 180-3, 180-4and 180-5, a write element 180-6, and a laser diode 180-7. The variouscomponents of the magnetic head 180 can be implemented using structuresand techniques that are well known in the art and consequently, adetailed explanation of such components is not necessary forunderstanding embodiments of the invention.

In general, the read circuits 234, 236, and 238 and respective readsensors 180-3, 180-4, and 180-5 are configured to read and processmagnetic signals that represent data stored on the storage medium 170.The read sensors 180-3, 180-4, and 180-5 are configured to sensemagnetic signals that exist on the storage medium 170, and output thesensed magnetic signals as continuous, minute analog signals (read backsignals) representative of the data that is stored on the storage medium170. The read circuits 234, 236, and 238 include circuitry such assensor bias sources to support the read sensors 180-3, 180-4 and 180-5,as well as low noise amplifiers to amplify the analog signals outputfrom the read sensors 180-3, 180-4 and 180-5. The read circuits 234,236, and 238 may include other circuitry that is commonly implemented toprocess read back signals.

FIG. 2 depicts an embodiment of a multi-dimensional recording system inwhich two or more read sensors are active during a read operation.Multi-dimensional recording techniques such as TDMR (Two DimensionalMagnetic Recording) have been developed to support higher bit densitiesin magnetic recording systems. With TDMR systems, two or more read headsare used to read the same track (and adjacent tracks) with a certainread offset, affording a degree of interference cancellation. TDMRenables the use of effective coding and signal processing algorithmsthat allow data bits to be stored at higher densities on a magneticstorage disk, and retrieved and decoded with acceptable error rates. Inthe example embodiment of FIG. 2, each of the three read sensors 180-3,180-4, and 180-5 are active during a read operation, thereby outputtingmultiple read back signals RD1, RD2, and RD3, which are concurrentlytransmitted from the preamplifier circuitry 130 to the recording channelcircuitry 110 over the analog bus 200.

In the recording channel circuitry 110, the read data circuitry 212concurrently receives and processes the read back signals RD1, RD2, andRD3. The read data circuitry 212 comprises various types of circuitryfor conditioning and digitizing the analog read back signals RD1, RD2,and RD3, and extracting a digital representation of the originallyrecorded data. For example, the read data circuitry 212 comprises analogfront-end circuitry for analog signal processing the read back signalsRD1, RD2, and RD3 received from the preamplifier circuitry 130 usingwell known circuits and analog signal processing techniques. Moreover,the read data circuitry 212 further comprises analog-to-digitalconverter circuitry that digitizes the analog signals, and othercircuitry such as data equalization circuitry, data detection circuitry,data decoding circuitry, data deserialization circuitry, clock recoverycircuitry, and other types of circuitry that is commonly included inrecording channels for processing and decoding the digitized read backsignals and recreating the digital data originally written to thestorage medium, the details of which are not necessary for understandingembodiment of the invention described herein.

The write data circuitry 214 in the recording channel circuitry 110 isconfigured to receive over the internal bus 116 data which is to bewritten to the storage medium 170, deserialize the write data, and thenencode, write precompensate, and otherwise transform the write data intoa form that can be recorded on the storage medium 170. The write datacircuitry 214 outputs encoded write data WD for transmission to thepreamplifier circuitry 130 over the analog bus 200. In the preamplifiercircuitry 130, the write circuitry 240 receives the encoded write dataWD and further processes the encoded write data WD, as desired, forrecording on the storage medium 170. The write circuitry 240 is furtherconfigured to drive the write element 180-6 in the magnetic head 180 forrecording the write data WD on the storage medium 170.

The pattern dependent write and/or heat assisted magnetic recordingcircuitry 242 (alternatively referred to individually as HAMR(heat-assisted magnetic recording) circuitry 242 or PDW (patterndependent write) circuitry 242) are circuits that are optionallyincluded in the preamplifier circuitry 130. Control and/or data signalsthat are used for controlling the pattern dependent write and/or heatassisted magnetic recording circuitry 242 are transmitted from therecording channel circuitry 110 to the preamplifier circuitry 130 overthe analog bus 200. As is known in the art, HAMR is an advancedrecording technology that enables a large increase in the storagedensity of hard disk drives. HAMR magnetically records data on amagnetic storage disk using a laser to heat the magnetic material of themagnetic storage disk before writing data to the magnetic storage disk,thus allowing the writer to magnetize high-coercivity media.

As depicted in FIG. 2, a laser clock signal LC for controlling a HAMRoperation is generated by the write data circuitry 214 and transmittedto the HAMR circuitry 242 over the analog bus 200. In the exampleembodiment of FIG. 2, the HAMR circuitry 242 uses the laser clock signalLC to generate a laser pulse signal at the transition rate of themagnetic write data WD to be recorded. The laser diode 180-7 is pulsedby the laser clock signal LC in synchronization with the data bits asthe data bits are written to the magnetic storage disk by operation ofthe write element 180-6, thereby temporarily heating a recording area ofthe magnetic storage medium 170 as data bits are written. This heatingprocess allows the write element 180-6 to more easily switch themagnetic orientation on the surface of the magnetic storage disk tostore the data bits. In one embodiment of the invention, the HAMRcircuitry 242 is implemented using the circuits and methods as disclosedin U.S. patent application Ser. No. 13/096,900, filed on Apr. 28, 2011,entitled Systems and Methods for Laser Write Control, which is commonlyassigned and incorporated herein by reference.

The PDW circuitry 242 is configured to generate a pattern dependentwrite control signal based on (i) a pattern in the write data WD that isreceived by the write circuitry 240 and (ii) an associated clock signalthat is generated by the write data circuitry 214 and transmitted to thepreamplifier circuitry 130 over the analog bus 200. The PDW circuitry242 is configured to set a write current level (in the write element180-6) to one of a plurality of different current levels based on thepattern dependent write control signal generated by the PDW circuitry242. The write data WD is then recorded on the magnetic storage medium170 using a write current through the write element 180-6 which has alevel (amplitude) that is set based on the pattern dependent writecontrol signal. The PDW process essentially modulates the write currentthat is used in the write element 180-6 to record the write data WD onthe magnetic storage medium 170, thereby compensating for magneticeffects which would otherwise degrade the written magnetic signal. Inone embodiment of the invention, the PDW circuitry 242 is implementedusing the circuits and methods as disclosed in U.S. patent applicationSer. No. 13/302,169, filed on Nov. 22, 2011, entitled Magnetic RecordingSystem With Multi-Level Write Current, which is commonly assigned andincorporated by reference herein. In another embodiment of theinvention, the PDW circuitry 242 is implemented using the circuits andmethods as disclosed in U.S. patent application Ser. No. 14/085,816,filed on Nov. 21, 2013, entitled Storage System With Pattern DependentWrite, which is commonly assigned and incorporated herein by reference.

The bit-patterned magnetic recording loopback circuitry 244 providessupport for embodiments in which the storage medium 170 is implementedusing patterned media. With patterned media technology, data is recordedin magnetic islands formed on the storage disk—a single data bit perisland. This is in contrast to hard disk drive technologies in whicheach data bit is stored in multiple grains (e.g., 20-30 magnetic grains)within a continuous magnetic film. With bit-patterned media recordingtechniques, each data bit is written on a small nanometer-sized magneticisland as the disk spins. With this recording mechanism, precisiontiming is needed to correctly write each bit on a respective magneticisland. In the example embodiment of FIG. 2, the bit-patterned magneticrecording loopback circuitry 244 is configured to generate a loop backsignal BP that is sent from the preamplifier circuitry 130 to therecording channel circuitry 110 over the analog bus 200. The write datacircuitry 214 processes the loopback signal BP to stabilize systemtiming for a bit-patterned recording process (e.g., ensure that phase ofdigital write signal is properly aligned to data bits of write data WD).

The fly height control circuitry 232 is configured to controllablyadjust the spacing (or fly height) between the magnetic head 180 and thesurface of the storage medium 170. In general, the fly height controlcircuitry 232, spacing sensor 180-1, and heater element 180-2 areconfigured to cooperate with elements of the recording channel circuitry110 and firmware that is operative within the hard disk controller 102to maintain a constant, low head-to-disk spacing that is needed forhigh-density recording. The fly height control circuitry 232 generatesand regulates either a programmed power level or voltage to the heaterelement 180-2 to control the heating of a region of the magnetic head180 (the “sensor region”) which contains the spacing sensor 180-1, theread sensors 180-3, 180-4, and 180-5, and the write element 180-6. Theheating of the sensor region causes the sensor region to bulge andthereby move the spacing sensor 180-1, the read sensors 180-3, 180-4,and 180-5, and the write element 180-6 closer to the surface of thestorage medium 170. The spacing sensor 180-1 generates a sensor currentwhich increases as the spacing sensor 180-1 approaches the surface ofthe storage medium 170. The sensor current generated by the spacingsensor 180-1 is processed by the fly height control circuitry 232 tocontrol the heater actuation process and, thus, control the spacingbetween the magnetic head 180 and the surface of the storage medium 170.

In the embodiment shown in FIG. 2, the read data RD1, RD2, and RD3, thewrite data WD, and the control signals LC and BP' are transmitted overthe analog bus 200 using a multiplexing interface that is implementedusing the multiplexing circuitry 204/206. The multiplexing circuitry204/206 allows the read data RD1, RD2, and RD3, the write data WD, andthe control signals LC and BP to share the analog signal lines of theanalog bus 200 connecting the recording channel circuitry 110 and thepreamplifier circuitry 130 so that the number of analog lines needed isless than the total number of different signals transmitted between therecording channel circuitry 110 and the preamplifier circuitry 130. Thisis in contrast to conventional storage systems in which each signal istransmitted between a recording channel and a preamplifier on adedicated unidirectional signal line. In the embodiment of FIG. 2, thevarious signals RD1, RD2, RD3, WD, LC, and BP are transmitted over a setof shared (multiplexed) bidirectional or unidirectional signal lines,wherein the multiplexing (sharing) and transmission direction of a givenline is determined based on whether a given recording operation is aread operation or a write operation.

In particular, in the embodiment of FIG. 2, the multiplexing circuitry204/206 comprises switching circuitry 204 located at one end of theanalog bus 200, and switching circuitry 206 located at an opposite endof the analog bus 200. The switching circuitry 204 comprises a pluralityof switches 204-1, 204-2, 204-3, 204-4, 204-5, and 204-6. The switchingcircuitry 206 comprises a plurality of switches 206-1, 206-2, 206-3,206-4, 206-5, and 206-6. As depicted in the example embodiment of FIG.2, the switches 204-1, 204-2, 206-1, and 206-2 control bidirectionaltransmission of multiplexed signals (e.g., read data RD1 and write dataWD) over the first analog signal line 200-1. Moreover, the switches204-3, 204-4, 206-3, and 206-4 control bidirectional transmission ofmultiplexed signals (e.g., read data RD2 and control signal LC) over thesecond analog signal line 200-2. Further, the switches 204-5, 204-6,206-5, and 206-6 control transmission of multiplexed signals (read dataRD3 and control signal BP) over the third analog signal line 200-3.

As depicted in FIG. 2, the multiplexing circuitry 204/206 is controlledby a write gate control signal (denoted +WRITE/−READ), which enables ordisables the various switches depending on the logic level of the writegate control signal. For example, in the embodiment of FIG. 2, during aread operation, the write gate control signal is set to logic “0”, whichenables the switches 204-1, 204-3, 204-5, 206-1, 206-3 and 206-5, andwhich disables the switches 204-2, 204-4, 204-6, 206-2, 206-4, and206-6. Thus, during a read operation, the read data RD1, RD2, and RD3are concurrently transmitted over respective analog lines 200-1, 200-2and 200-3 of the analog bus 200 from the preamplifier circuitry 130 tothe recording channel circuitry 110.

On the other hand, during a write operation, the write gate controlsignal is set to logic “1”, which disables the switches 204-1, 204-3,204-5, 206-1, 206-3 and 206-5, and which enables the switches 204-2,204-4, 204-6, 206-2, 206-4, and 206-6. Therefore, during a writeoperation, the write data WD and control signal LC are transmitted overrespective analog lines 200-1 and 200-2 of the analog bus 200 from therecording channel circuitry 110 to the preamplifier circuitry 130, andthe control signal BP is transmitted over the analog line 200-3 from thepreamplifier circuitry 130 to the recording channel circuitry 110.

In the embodiment of FIG. 2, the first analog line 200-1 is implementedas a multiplexed bidirectional line as follows. During a read operation,a first input of the read data circuitry 212 is switchably connected tothe first analog line 200-1 (via the enabled switch 204-1) to receiveread data RD1 transmitted from the preamplifier circuitry 130 over thefirst analog line 200-1. On the other hand, during a write operation, awrite data output of the write data circuitry 214 is switchablyconnected to the first analog line 200-1 (via the enabled switch 204-2)to transmit write data WD from the recording channel circuitry 110 overthe first analog line 200-1.

Moreover, the second analog line 200-2 is implemented as a multiplexedbidirectional line as follows. During a read operation, a second inputof the read data circuitry 212 is switchably connected to the secondanalog line 200-2 (via the enabled switch 204-3) to receive read dataRD2 transmitted from the preamplifier circuitry 130 over the secondanalog line 200-2. On the other hand, during a write operation, a writecontrol output of the write data circuitry 214 is switchably connectedto the second analog line 200-2 (via the enabled switch 204-4) totransmit a write control signal (e.g., laser clock signal LC) to thepreamplifier circuitry 130 over the second analog line 200-2.

Further, the third analog line 200-3 is implemented as a multiplexedunidirectional line as follows. During a read operation, a third inputof the read data circuitry 212 is switchably connected to the thirdanalog line 200-3 (via the enabled switch 204-5) to receive read dataRD3 transmitted from the preamplifier circuitry 130 over the thirdanalog line 200-3. On the other hand, during a write operation, a writecontrol input of the write data circuitry 214 is switchably connected tothe third analog line 200-3 (via the enabled switch 204-6) to receive awrite control signal (e.g., loop back control signal BP) transmittedfrom the preamplifier circuitry 130 over the third analog line 200-3.

In general, the digital bus 202 is controlled by the synchronous serialport control circuitry 112 and the port logic circuitry 226 in thepreamplifier circuitry 130. The port logic circuitry 216 (master) in thesynchronous serial port control circuitry 112 operates in conjunctionwith the port logic circuitry 226 (slave) in the preamplifier circuitry130 to control multiplexed, bidirectional transfer of digital signals(PDATA) over the bidirectional serial data line 202-1 of the digital bus202. In particular, the multiplexing circuitry 208/210 comprisesswitching circuitry 208 located at one end of the bidirectional serialdata line 202-1, and switching circuitry 210 located at an opposite endof the bidirectional serial data line 202-1. The switching circuitry 208comprises switches 208-1 and 208-2, and the switching circuitry 210comprises switches 210-1 and 210-2.

As depicted in FIG. 2, the multiplexing circuitry 208/210 is controlledby a direction control signal (denoted +D/−D), which enables or disablesthe various switches depending on the logic level of direction controlsignal. For example, to transmit PDATA in an “outbound” direction (fromthe synchronous serial port control circuitry 112 to the preamplifiercircuitry 130), the direction control signal +D/−D is set to logic “0”,which enables the switches 208-1 and 210-2, and which disables theswitches 208-2 and 210-1. On the other hand, to transmit PDATA in an“inbound” direction (to the synchronous serial port control circuitry112 from the preamplifier circuitry 130), the direction control signal+D/−D is set to logic “1”, which disables the switches 208-1 and 210-2,and which enables the switches 208-2 and 210-1.

The bidirectional serial data line 202-1 and associated clock signalline 202-2 provide a high-speed bidirectional synchronous serial portframework which is utilized to perform all preamplifier register setupand interrogation operations, as well as functions traditionallyperformed by dedicated bit-significant lines and other dedicated serialport control lines to control register access and sequencing functionsin the preamplifier circuitry 130.

The port logic circuitry 216 (master) and port logic circuitry 226(slave) operate the bidirectional serial data line 202-1 of the digitalbus 202 in essentially a mater/slave manner to transmit digitalinformation signals back and forth between the synchronous serial portcontrol circuitry 112 and preamplifier circuitry 130. The port logiccircuitry 216 (master) receives digital information signals (data andcontrol) from the internal bus 116 including, for example, registerdata, mode control signals, register read commands, fly height controldata, etc., and the port control circuitry 216 (master) transmitsregister setup information, read/write mode signals, and flyheight-heater demand signals, for example, in an “outbound” direction tothe preamplifier circuitry 130 over the bidirectional serial data line202-1. On the other hand, the port control circuitry 226 (slave)transmits, e.g., register read results, fault polling, and head/discspacing (fly height) information, and other information discussed below,in an “inbound” direction to the synchronous serial port controlcircuitry 112 over the bidirectional serial data line 202-1.

Moreover, the clock generator 218 generates a synchronous clock signal(PCLOCK) that is transmitted on the clock signal line 202-2 of thedigital bus 202 from the synchronous serial port control circuitry 112to the preamplifier circuitry 130 to synchronize transfer and processingof the digital signals (PDATA) transmitted on the bidirectional serialdata line 202-1 of the digital bus 202. The PCLOCK signal transmitted onthe clock signal line 202-2 is used by preamplifier circuitry 130 tocontrol timing of sequence control functions that are implemented by,e.g., the port logic circuitry 115, the gap detector circuit 228, thephase detector circuit 230, etc. The clock generator 218 generates thePCLOCK signal based on a clock signal CLK that is received over theinternal bus 116. The clock signal CLK is also used to controlsequencing functions in the port logic circuitry 216. The clock signalCLK can be an external clock signal generated by a PLL (phase lockedloop) circuit implemented by a microprocessor. The clock signal CLK canbe fixed or programmable. Moreover, since the synchronous serial port isfully synchronous, the PCLOCK signal can be paused at any timeconsistent with the required port activity and the potential use ofPCLOCK as the master clock in the sequencing logic of the preamplifiercircuitry 130.

In response to a control signal from the port logic circuitry 216, theclock generator 218 is configured to temporarily disable generation ofclock pulses of the PCLOCK signal for a given period of time so as toinsert a “gap” within the PCLOCK signal stream. The gap detector circuit228 in the preamplifier circuitry 130 is configured to detect a gap inthe PCLOCK signal stream. In one embodiment of the invention asdiscussed in further detail below with reference to FIG. 7, for example,the “gap” within the PCLOCK signal stream is used as a direction switchcontrol signal that instructs the port logic circuitry 226 to gaincontrol of the bidirectional serial data line 202-1 to transmit digitalinformation to the synchronous serial port control circuitry 112. Inanother embodiment of the invention as discussed in further detail withreference to FIG. 10, for example, the “gap” within the PCLOCK signalstream is used as a reset control signal that instructs the preamplifiercircuitry 130 to perform a reset operation to reset the preamplifiercircuitry 130.

Moreover, the clock generator 218 comprises circuitry for adjusting thefrequency of the PCLOCK signal that is transmitted over the clock signalline 202-2. For example, the clock generator 218 can generate a PCLOCKsignal having a high frequency (e.g., 1-2 GHz) for use in synchronizinghigh-rate transmission of digital PDATA streams to the preamplifiercircuitry 130 under normal operating conditions. The clock generator 218comprises circuitry (e.g., clock divider circuitry) for throttling downthe frequency of the PCLOCK signal to a lower frequency (e.g., 100 MHz)in instances where it is desired to synchronizing low-rate transmissionof digital PDATA streams between the synchronous serial port controlcircuitry 112 and the preamplifier circuitry 130 to enable reliablecommunication.

For example, in one embodiment of the invention, the PCLOCK signal isthrottled down to a lower frequency during a “skew measurement” processthat is implemented by the synchronous serial port control circuitry 112and preamplifier circuitry 130 operating in collaboration to measure atime skew between PDATA and PCLOCK signals transmitted on thebidirectional serial data line 202-1 and the clock signal line 202-2 ofthe digital bus 202, and phase aligning the PDATA and PCLOCK signalstreams based on skew measurement results. The preamplifier circuitry130 comprises skew measurement circuitry that is collectivelyimplemented by the port logic circuitry 226 and phase detector circuitry230 to perform a skew measurement process and transmit the skewmeasurement results to the port logic circuitry 216 (master). Based onthe skew measurement results, the port logic circuitry 216 controls thealignment circuitry 220 to adjust the phase of PCLOCK signal to vary thealignment of the PCLOCK signal (transmitted on the clock signal line202-2) with the digital PDATA stream (transmitted on the bidirectionalserial data line 202-1).

In one embodiment of the invention, the frequency of the PCLOCK signalis throttled down (by operation of the clock generator 218) so that theport logic circuitry 226 (slave) can reliably detect the measure skewcontrol signal transmitted on the bidirectional serial data line 202-1from the synchronous serial port control circuitry 112, and so that theport logic circuitry 216 (master) can reliably detect the skewmeasurement result transmitted from the preamplifier circuitry 130 onthe bidirectional serial data line 202-1. Example embodiments of theskew measurement process and related circuitry will be discussed infurther detail below with reference to FIGS. 8, 9, and 10, for example.

The port logic circuitries 216 and 226 include type of logic circuits toperform their respective functions. For example, the port logiccircuitries 216 and 226 each comprise serializer/deserializer (SerDes)circuitry to serialize digital data that is transmitted over thebidirectional serial data line 202-1, and to parallelize digital datathat is received over the bidirectional serial data line 202-1. Forexample, blocks of parallel register data received by the port logiccircuitry 216 over the internal bus 116 are converted to serial registerdata for transmission to the preamplifier circuitry 130 over thebidirectional serial data line 202-1 of the digital bus 202.

Moreover, the port logic circuitries 216 and 226 include encoder anddecoder circuits to encode and decode data that is transmitted on thebidirectional serial data line 202-1 based on a signal line codeprotocol implemented for the given application. For instance, in oneembodiment of the invention, the PDATA can be transmitted on thebidirectional serial data line 202-1 using an 8 b/10 b coding protocol.As is known in the art, 8 b/10 b encoding is a protocol in which eacheight-bit data byte is converted to a 10-bit transmission character. Theencoding process provides 256 data characters, as well as 12 uniquenon-data control characters. Other line coding protocols may beimplemented.

In the preamplifier circuitry 130, the register data is stored withinregister banks in the register bank and command logic circuitry 246. Theregister bank and command logic circuitry 246 is controlled by a clocksignal CLK output from the port logic circuitry 226. The clock signalCLK can be a buffered version of the synchronous PCLOCK signal that isused to control sequencing operations of the port logic circuitry 226.The port logic circuitry 226 can send register data to the register bankand command logic circuitry over a parallel bus 248 for storage in oneor more register banks. The port logic circuitry 226 can read/accessregister data that is stored in one or more register banks of theregister bank and command logic circuitry 246 and transmit theread/accessed register data to the synchronous serial port controlcircuitry 112 over the bidirectional serial data line 202-1.

The register bank and command logic circuitry 246 comprises controlcircuitry to generate control signals that control operation of thevarious components 206, 232, 234, 236, 238, 240, 242 and 242 of thepreamplifier circuitry 130 based on configuration data stored in theregister banks, for example. Moreover, the register bank and commandlogic circuitry 246 can generate the write gate control signal(+WRITE/−READ) which is used to control the multiplexing circuitry 206.

It is to be understood that FIG. 2 is merely an illustrative embodimentto show different types of data and control signals that can betransmitted over multiplexed signal lines of the analog bus 200 anddigital bus 202. The types of signals that are transmitted between therecording channel circuitry 110 and the preamplifier circuitry 130, andtransmitted between the synchronous serial port control circuitry 112and the preamplifier circuitry 130, will vary depending on the givenapplication and particular implementation of the storage device. Forexample, FIG. 3 illustrates another embodiment of the storage device ofFIG. 1, which comprises circuitry to support multiplexed communicationin the storage device. FIG. 3 is similar to FIG. 2 except that theembodiment of FIG. 3 illustrates a multiplexing scheme to supporttwo-dimensional encoded writing.

In particular, as depicted in FIG. 3, the write data circuitry 214generates two write data signals WD and WD_2, which are transmitted(during a write operation) to write circuitry 340 in the preamplifiercircuitry 130 over the first and second analog lines 200-1 and 200-2,respectively. The write circuitry 340 in the preamplifier circuitry 130comprises circuitry for processing the write data WD and WD_2 anddriving separate write elements 180-6 and 180-8 to write data ondifferent tracks of the storage disk. A multi-dimensional encoding writeprotocol as generally depicted in FIG. 3 enables the writing ofdifferent encoded data with different spectral content on adjacenttracks, which helps to distinguish the stored data on different tracks(in higher-storage density applications) and access the stored data withlow BERs (bit error rates). As further depicted in FIG. 3, the thirdanalog signal line 200-3 is implemented as a multiplexed bidirectionalline (as compared to a multiplexed unidirectional line as depicted inFIG. 2), wherein read data RD3 is transmitted to the recording channelcircuitry 110 over the third analog line 200-3 during a read operation,and wherein the write control signal LC is transmitted to thepreamplifier circuitry 130 over the third analog line 200-3 during awrite operation.

In each of the embodiments of FIGS. 2 and 3, the number of individualsignal lines that are used in the analog bus 200 and digital bus 202 isless than a total number of information signals (control and datasignals) that are transmitted between the preamplifier circuitry 130 andthe recording channel circuitry 110, and between the synchronous serialport control circuitry 112 and the preamplifier circuitry 130. By way ofspecific example, with regard to the analog bus 200, FIG. 4 is a tablethat comparatively illustrates a number of signal lines needed for anon-multiplexed analog bus as compared to a number of signal lines usedfor a multiplexed analog bus according to alternate embodiments of theinvention. In particular, FIG. 4 comparatively illustrates alternateembodiments for multiplexing read data, write data, and control signalsfor a three-channel multi-dimensional recording storage device.

As shown in FIG. 4, for a basic embodiment, a non-multiplexed schemewould require four (4) separate signal lines (e.g. four differentialpairs) to transmit three read data signals RD1, RD2 and RD3 and onewrite data signal WD. In contrast, for a multiplexed scheme, the basicembodiment would utilize three (3) signal lines as the write data signalWD and read data signal RD1 could share the same signal line. As furthershown in FIG. 4, for a basic embodiment with added pulsed HAMR or PDW, anon-multiplexed scheme would require five (5) separate signal lines(e.g., five differential pairs). In contrast, for a multiplexed scheme,the basic embodiment with added pulsed HAMR or PDW would utilize three(3) signal lines as the write data signal

WD and read data signal RD1 could share the same signal line, and thecontrol signal LC and read data signal RD2 could share the same signalline. Moreover, as further shown in FIG. 4, for a basic embodiment withadded BPM and pulsed HAMR or PDW, a non-multiplexed scheme would requiresix (6) separate signal lines (e.g., six differential pairs). Incontrast, for a multiplexed scheme, the basic embodiment with added BPMand pulsed HAMR or PDW would utilize three (3) signal lines as the writedata signal WD and read data signal RD1 could share the same signalline, the control signal LC and read data signal RD2 could share thesame signal line, and the control signal BP and read data signal RD3could share the same signal line.

It is to be understood that a data storage device such as depicted inFIGS. 2 and 3 can implement both the analog bus 200 and digital bus 202and associated multiplexing circuitries and control interfaces, asdiscussed herein. In another embodiment, a data storage device canimplement either the analog bus 200 or the digital bus 202 (andassociated multiplexing circuitry and control interface) exclusive, andindependent from each other. For instance, the analog bus 200 andassociated multiplexing circuitry 204/206 and control interface, asshown in FIGS. 2 and 3, can be used to implement multiplexedcommunication between the recording channel circuitry 110 and thepreamplifier circuitry 130, while a conventional serial portarchitecture can be used to implement non-multiplexed communicationbetween a controller and the preamplifier circuitry 130.

For example, the digital bus 202 (and associated multiplexing circuitry208/210 and control interface) as shown in FIGS. 2 and 3 can be replacedwith a conventional non-multiplexed three wire synchronous serial portcomprising a (i) clock signal line, (ii) bidirectional serial data line,and an (iii) enable line to transmit setup and status monitoringinformation of configuration registers located in the preamplifiercircuitry 130, together with one or more additional dedicated digitallines to transmit respective bit-significant control signals such as amode control signal, a write gate control signal, and fault pollingcontrol signal, for example. By way of example, in this embodiment, thewrite gate (+WRITE/−READ) control signal shown in FIGS. 2 and 3 wouldnot be transmitted on the bidirectional serial data line 202-1 of thedigital bus 202. Instead, the write gate (+WRITE/−READ) control signalwould be transmitted on a dedicated bit-significant line separate fromthe conventional three-wire serial port. Indeed, in a conventionalcommunication scheme between a controller and preamplifier, digitalfunctions such as write gate, fault polling and mode control functionsrequiring immediate attention, which cannot tolerate the polling andlatency characteristics of a conventional serial port, would betransmitted on a bit-significant basis on an additional control buscomprising dedicated bit-significant control lines, separate from theserial port.

Furthermore, in another embodiment of the invention, the analog bus 200(and associated multiplexing circuitry 204/206 and control interface) asshown in FIGS. 2 and 3 can be replaced with a conventionalnon-multiplexed analog bus, while utilizing the two-wire, multiplexedsynchronous serial port shown in FIGS. 2 and 3. In this embodiment, thenon-multiplexed analog bus would have a dedicated signal line for eachread back signal and write signal transmitted between the recordingchannel and preamplifier, such as shown in FIG. 4, for example.

FIG. 5 is a flow diagram of a method to implement communication betweena controller and a preamplifier in a storage device using a digital buscomprising a single bidirectional serial data line and a single clocksignal line, according to an embodiment of the invention. In general,the method shown in FIG. 5 comprises controlling a bidirectional serialdata line of a digital bus to selectively transmit digital signals ineither a first direction from the controller to the preamplifier or asecond direction from the preamplifier to the controller, in response toa direction control signal (block 500), while concurrently transmittinga synchronous clock signal over a clock signal line of the digital busfrom the controller to the preamplifier to synchronize transfer andprocessing of the digital signals transmitted on the bidirectionalserial data line of the digital bus (block 502). For purposes ofillustration, the method of FIG. 5 will be discussed in further detailbelow with reference to the exemplary embodiment of FIGS. 2. 6, and 7,for example, in the context of controlling communication between thesynchronous serial port control circuitry 112 and the preamplifiercircuitry 130 over a synchronous serial port.

As noted above, the port logic circuitry 216 (master) in the synchronousserial port control circuitry 112 operates in conjunction with the portlogic circuitry 226 (slave) in the preamplifier circuitry 130 to controlmultiplexed, bidirectional transfer of digital signals

(PDATA) over the bidirectional serial data line 202-1 of the digital bus202. Moreover, the port logic circuitry 216 controls the clock generator218 to generate a synchronous clock signal PCLOCK that is transmittedover the clock signal line 202-2 of the digital bus 202 to controlsequencing functions in preamplifier circuitry 130 (e.g., control theport logic circuitry 226, the gap detector circuit 228, the phasedetector circuitry 230, etc.). In accordance with embodiments of theinvention, the transmission direction of PDATA is controlled by thesynchronous serial port control circuitry 112 inserting directioncontrol characters in either an outbound PDATA stream or in the PCLOCKsignal. For example, FIGS. 6 and 7 are timing diagrams that illustratemethods to control a direction switch on a bidirectional serial dataline according to alternate embodiments of the invention.

In particular, FIG. 6 is a timing diagram that illustrates a method tocontrol a direction switch on a bidirectional serial data line byinserting a direction control character in an outbound PDATA stream,according to an embodiment of the invention. In the context of theembodiment of FIG. 2, for example, FIG. 6 illustrates an example PCLOCKsignal 600 and a PDATA stream 610 which are transmitted on the clocksignal line 200-2 and the bidirectional serial data line 202-1,respectively, of the digital bus 202. As shown in FIG. 6, the PDATAstream 610 comprises a plurality of data blocks 612, 614, 616, 618, and620, and a direction control character 630 (DCC). The arrows in FIG. 6denote a transmission direction of the data blocks 612, 614, 616, 618,and 620 and the direction control character 630. The data blocks 612,614, 618 and 620 and direction control character 630 are shown as beingtransmitted in an outbound direction from a controller to a preamplifier(e.g., from the synchronous serial port control circuitry 112 to thepreamplifier circuitry 130, FIG. 2). On the other hand, the data block616 is shown as being transmitted in an inbound direction from thepreamplifier to the controller (e.g. from the preamplifier circuitry 130to the synchronous serial port control circuitry 112).

It is to be noted that the data blocks 612, 614, 61,8 and 620transmitted from the controller to the preamplifier include actualblocks of data (e.g., register data, register address information, etc.)and/or control signals. For example, as noted above with reference toFIG. 2, in an outbound direction, one or more of the data blocks 612,614, 618, and 620 can include register data (preamplifier configurationdata and an associated register address) that is received by the portlogic circuitry 216 (master) and transmitted to the preamplifiercircuitry 130 for storage in one or more register banks of the registerbank and command logic circuitry 246. Moreover, one or more of the datablocks 612, 614, 618 and 620 can include control signals such aswrite/read mode signals, and fly height heater control signals, registerread control signals, etc., which are used to control certain functionsof the preamplifier circuitry 130. In the inbound direction from thepreamplifier to the controller, the data block 616 can includeinformation such as configuration data, fault polling, head/disc spacinginformation measured by the fly height control circuitry 232, or otherstatus information that is stored in register banks of the preamplifiercircuitry, and accessed by the controller and recording channel. In oneembodiment, the outbound direction is afforded a higher priority thanthe inbound direction because mode control and register loadingfunctions are more time-critical than register read and pollingoperations, for example.

When certain information (register data, etc.) from the preamplifiercircuitry 130 is desired, the port logic circuitry 216 (master) insertsthe direction control character 630 into the PDATA stream to signal adirection switch for the port logic circuitry 226 (slave) to transmitdigital signals on the bidirectional serial data line 202-1 to thesynchronous serial port control circuitry 112. In one embodiment of theinvention, the direction control character 630 comprises an initiateregister read command together with register address data that specifiesan address of the register from which data (or a pointer to anotherregister) is to be read. In such embodiment, a direction switch isimplied by the direction control character 630 that initiates a registerread, and causes the preamplifier circuitry 130 to initiate control ofthe bidirectional serial line 202-1 to return the register read results.In another embodiment, the direction control character 630 can include aregister address and byte count information for sequentially accessingregister data from a series of registers. For instance, assume that eachregister stores a byte of data. If the control character 630 specifies aregister address of 5 and byte count of 3, this command directs thepreamplifier circuitry 130 to access the contents of a register withaddress 5, and the contents of the next three sequential registers 6, 7and 8.

In another embodiment of the invention, the direction control character630 may be a stand-alone direction control character that implies adirection switch for a register read command, wherein the registeraddress (and possible byte count information) are transmitted on thebidirectional serial data line 202-1 just prior to the direction controlcharacter 630 or just after the direction control character 630. Forexample, in FIG. 6, the data block 614 just prior to the directioncontrol character 630 can specify a register address that is to be readin response to the register read operation that is initiated by thedirection control character 630. Moreover, the data block 612 canspecify a register address and the data block 614 could specify a bytecount. In such instance, the preamplifier circuitry 130 would know thatthe last received register address information block corresponds to theread command to be initiated in response to the direction controlcharacter 630. In another embodiment, the register address informationand associated byte count can serially transmitted in data blocksfollowing the stand-alone direction control character.

After the direction control character 630 (and an associated registeraddress and possible byte count information) is transmitted, the portlogic circuitry 216 (master) relinquishes control of the bidirectionalserial data line 202-1 by asserting a logic “1” direction control signal(+D/−D) to the multiplexing circuitry 208, which disables themultiplexer switch 208-1 and enables the multiplexer switch 208-2.During a period of time 640 following transmission of the directioncontrol character 630 (and associated register address data and possiblebyte count), the port logic circuitry 226 (slave) asserts control of thebidirectional serial data line 202-1 by asserting a logic “1” directioncontrol signal (+D/−D) to the multiplexing circuitry 210, which enablesthe multiplexer switch 210-1 and disables the multiplexer switch 210-2,and thereupon transmits data accessed from the addressed register.

In addition, during the period of time 640 following transmission of thedirection control character 630, the preamplifier circuitry 130 performssome sequencing operations (under control of the port logic circuitry226 (slave) and the PCLOCK signal 600) to obtain the requestedinformation for transmission back to the port logic circuitry 216(master) over the bidirectional serial data line 202-1. Once therequested information is obtained, the port logic circuitry 226 (slave)serially transmits one or more data blocks (e.g., data block 616) to theport logic circuitry 216 (master) over the bidirectional serial dataline 202-1.

During a period of time 650 following transmission of the data block616, the port logic circuitry 226 (slave) relinquishes control of thebidirectional serial data line 202-1 by asserting a logic “0” directioncontrol signal (+D/−D) to the multiplexing circuitry 210, which disablesthe multiplexer switch 210-1 and enables the multiplexer switch 210-2.Furthermore, during the period of time 650, the port logic circuitry 216(master) asserts control of the bidirectional serial data line 202-1 byasserting a logic “0” direction control signal (+D/−D) to themultiplexing circuitry 208, which enables the multiplexer switch 208-1and disables the multiplexer switch 208-2. Because of the synchronouscontrol by PCLOCK 600, and because the port logic circuitry 216 (master)knows a priori how may bits of information will be transmitted inresponse to a request for information, the port logic circuitry 216(master) knows when the transmission of the data block 616 over thebidirectional serial data line 202-1 is complete. For example, if aregister read request is sent to the preamplifier circuitry 130 to readthe contents of 5 registers in a register bank, and each register is onebyte in length, then upon transmission of the register read results fromthe preamplifier circuitry 130 to the synchronous serial port controlcircuitry 112, the port logic circuitry 216 (master) would except toreceive a serial data block 5 bytes in length.

The direction control character 630 can be generated using differenttechniques. For example, in one embodiment of the invention, thedirection control character 630 comprises a 8 b/10 b code. As notedabove, 8 b/10 b encoding is a protocol in which each eight-bit data byteis converted to a 10-bit transmission character. The encoding processprovides 256 data characters, as well as 12 unique non-data controlcharacters. In accordance with embodiments of the invention, the 8 b/10b characters are used for identifying management functions or control.In accordance with an embodiment of the invention where outbound datatransmitted over the bidirectional serial data line 202-1 is encodedusing an 8 b/10 b code, the direction control character 630 may bechosen from surplus characters that are not used to encode data bytes.Since PDATA is dc coupled and not self-clocked, and transmissiondistances short, where spectral and maximum-run-length characteristicsare not an issue, it is possible to simplify the codebook for the 8 b/10b encoding process.

In another embodiment of the invention, a direction control signal isinserted in the PCLOCK signal as a way to specify a direction switch tothe preamplifier circuitry 130. For example, FIG. 7 is a timing diagramthat illustrates a method to control a direction switch on abidirectional serial data line by inserting a gap in PCLOCK signalstream according to an embodiment of the invention. In the context ofthe embodiment of FIG. 2, for example, FIG. 7 illustrates an examplePCLOCK signal 700 and a PDATA stream 710 which are transmitted on theclock signal line 202-2 and the bidirectional serial data line 202-1,respectively, of the digital bus 202. As shown in FIG. 7, the PCLOCKsignal 700 comprises a gap 702 that represents a predefined number ofdeleted clock cycles. The PDATA stream 710 comprises a plurality of datablocks 712, 714, 716, 718, and 720, and a control character 730. Thearrows in FIG. 7 denote a transmission direction of the data blocks 712,714, 716, 718, and 720 and the control character 730 between thecontroller and preamplifier (e.g., between the synchronous serial portcontrol circuitry 112 and the preamplifier circuitry 130 of FIG. 2).

In the context of the embodiment of FIG. 2, the gap 702 is generated inthe PCLOCK signal 700 by the clock generator 218 under command by theport logic circuitry 216 (master) and transmitted over the clock signalline 202-2 of the digital bus 202. In one embodiment, the clockgenerator 218 generates the gap 702 by deleting or otherwise suppressinga predetermined number of clock cycles of the PCLOCK signal 700, whichis sufficient to allow reliable detection by the gap detector circuit228 in the presence of timer tolerances. In the preamplifier circuitry130, the gap 702 is detected by the gap detector circuit 228, whereinthe gap detector circuit 228 outputs a gap detection signal to the portlogic circuitry 226 (slave) upon detection of the gap 702.

In one embodiment of the invention, the gap detector circuit 228 is anasynchronous timer that operates to detect the gap 702 based on apredetermined amount of time that no clock pulses are detected for thePCLOCK signal 700, wherein the timer resets upon each positive edge of areceived clock pulse, for example. The gap detector circuitry 228 can beimplemented using other circuits that are suitable for the given gapdetection application.

When the gap 702 is generated to trigger a direction switch of theserial port, the port logic circuitry 216 (master) stops transmittinginformation signals on the bidirectional serial data line 202-1. Inparticular, as shown in FIG. 7, during the period in which the gap 702is generated in the PCLOCK signal 700, there is a corresponding periodof time 740 in which no information is transmitted via the PDATA stream710 to the preamplifier circuitry 130. After the gap 702 is generated,the PCLOCK signal 700 is commenced, and the port logic circuitry 216(master) transmits the control character 730 (e.g., register readcommand, etc.) to the preamplifier circuitry 130. The detection of thegap 702 by the gap detector circuit 228 in the preamplifier circuitry130 causes the initiation of the operation specified by the controlcharacter 730 upon the occurrence of the next rising edge of the PCLOCKsignal 700 following the gap 702. The control character 730 specifiesthe register address to be read, and possible a byte count. Theoccurrence of the gap 702 implies that the, next character received bythe preamplifier circuitry 130 is the control character 730.

During a period of time 750 following transmission of the controlcharacter 730, the port logic circuitry 216 (master) relinquishescontrol of the bidirectional serial data line 202-1 by asserting a logic“1” direction control signal (+D/−D) to the multiplexing circuitry 208,which disables the multiplexer switch 208-1 and enables the multiplexerswitch 208-2. In addition, during the period of time 750 followingtransmission of the control character 730, the port logic circuitry 226(slave) asserts control of the bidirectional serial data line 202-1 byasserting a logic “1” direction control signal (+D/−D) to themultiplexing circuitry 210, which enables the multiplexer switch 210-1and disables the multiplexer switch 210-2.

Furthermore, during the period of time 750 following transmission of thecontrol character 730, the preamplifier circuitry 130 performs somesequencing operations (under control of the port logic circuitry 226(slave) and the PCLOCK signal 700) to obtain the requested informationfor transmission back to the port logic circuitry 216 (master) over thebidirectional serial data line 202-1. Once the requested information isobtained, the port logic circuitry 226 (slave) serially transmits one ormore data blocks (e.g., data block 716) to the port logic circuitry 216(master) over the bidirectional serial data line 202-1.

During a period of time 760 following transmission of the data block 716from the preamplifier circuitry 130 to the synchronous serial portcontrol circuitry 112, the port logic circuitry 226 (slave) relinquishescontrol of the bidirectional serial data line 202-1 by asserting a logic“0” direction control signal (+D/−D) to the multiplexing circuitry 210,which disables the multiplexer switch 210-1 and enables the multiplexerswitch 210-2. Furthermore, during that period of time 760, the portlogic circuitry 216 (master) asserts control of the bidirectional serialdata line 202-1 by asserting a logic “0” direction control signal(+D/−D) to the multiplexing circuitry 208, which enables the multiplexerswitch 208-1 and disables the multiplexer switch 208-2. Because of thesynchronous control by PCLOCK 700, and because the port logic circuitry216 (master) knows a priori how may bits of information will betransmitted in response to a request for information, the port logiccircuitry 216 (master) knows when the transmission of the data block 716over the bidirectional serial data line 202-1 is complete.

In the embodiment of FIG. 7, 8 b/10 b-like coding is unnecessary, as thegap 702 in the PCLOCK signal 700 serves as a direction-change demarker.An advantage to using the gap detection process of FIG. 7 is that itsupports forced abort of transfer operations in progress, reducinglatency of mode changes, and provides an unambiguous periodicinitialization of serialization/deserialization counters in thepreamplifier circuitry 130. When using a gap detection process, thePCLOCK signal 700 continuously runs, except when a gap is generated.

In other embodiments of the invention, circuits and methods as disclosedin U.S. patent application Ser. No. 13/650,474, filed on Oct. 12, 2012,entitled Preamplifier-To-Channel Communication in a Storage Device, andU.S. patent application Ser. No. 13/719,615, filed on Dec. 19, 2012,entitled Tag Multiplication Via A Preamplifier Interface, can beimplemented in the port logic circuitry 216 (master) and/or port logiccircuitry 226 (slave) for generating and merging bit significant signalswithin a synchronous serial port framework supported by the digital bus202 as discussed above with reference to FIGS. 2 and 3. Theseapplications are commonly assigned and fully incorporated herein byreference. In general, U.S. patent application Ser. No. 13/650,474discloses methods for merging bit significant signals onto a unifiedhigh-speed serial port. Moreover, U.S. patent application Ser. No.13/719,615 discloses methods for generating additional bit significantsignals within the preamplifier circuitry without the need foradditional signaling wires.

In one embodiment of the invention, to minimize transaction time andlatency over the synchronous serial communication port, the PCLOCKsignal operates at a high frequency, e.g., 1-2 GHz (i.e., 1-2 Gbit/seetransfer rate). In one embodiment, the synchronous serial data port andassociated sequencing functions operate on a rising clock edge ofPCLOCK, although in other embodiments, the synchronous serial data portand associated sequencing functions can operate on both the rising andfalling clock edges of PCLOCK. When operating a synchronous serialcommunication port with high-speed clocking (e.g., 1-2 GHz), it isdesirable to maintain reliable communication over the serial portdespite possible time skewing between the PDATA bit stream and thePCLOCK signal. Indeed, when a serial data stream (PDATA) is captured ina receiving flip-flop circuit that is clocked by the associatedsynchronous clock signal (PCLOCK), the existence of time skew betweenthe PCLOCK and PDATA signal streams can adversely affect the ability ofthe receiving flip-flop to receive every transmitted data bit, which canthereby degrade the reliability of data transfer at high-speed clockrates. Accordingly, in one embodiment of the invention, the synchronousserial port control circuitry 112 and preamplifier circuitry 130 operatein collaboration to measure skew between the PCLOCK and PDATA streamsand align the streams based on the measured skew.

For example, FIG. 8 is a flow diagram of skew measurement method that isimplemented by a serial port controller and preamplifier to align asynchronous clock signal with digital signals to be transmitted over abidirectional serial data line using a skew measurement protocol,according to an embodiment of the invention. For purposes ofillustration, the method of FIG. 8 will be discussed with reference tothe storage device embodiments depicted in FIGS. 2 and 3, wherein themethod is implemented to provide reliable communication between thesynchronous serial port control circuitry 112 and the preamplifiercircuitry 130 in the presence of skew between a PDATA stream and anassociated PCLOCK signal.

Referring to FIG. 8, an initial step is to initiate reset of thepreamplifier circuitry 130 (block 800). Various methods forresetting/initializing the preamplifier circuitry 130 will be discussedin further detail below with reference to FIGS. 10 and 11, for example.Following reset of the preamplifier circuitry 130, a synchronous clocksignal (PCLOCK) is transmitted over the clock signal line 202-1 of thedigital bus 202 from the synchronous serial port control circuitry 112to the preamplifier circuitry 130, wherein the synchronous clock signal(PCLOCK) is initially transmitted at a first frequency which is lessthan a normal operating frequency of the synchronous serial data port(block 802). As explained above, the synchronous clock signal (PCLOCK)synchronizes the transfer and processing of digital signals (PDATA)transmitted on the bidirectional serial data line 202-1 of the digitalbus 202.

Next, a digital control signal (Measure_Skew control character) and askew calibration stream (e.g., skew calibration clock signal) areserially transmitted on the bidirectional serial data line 202-1 fromthe synchronous serial port control circuitry 112 to the preamplifiercircuitry 130 (block 804). The digital control signal (Measure_Skewcontrol character) is a control character that instructs thepreamplifier circuitry 130 to measure skew between the synchronous clocksignal (PCLOCK) transmitted on the clock signal line 202-2 and the skewcalibration stream transmitted on the bidirectional serial data line202-1. In response to the digital control signal, the preamplifiercircuitry 130 measures the skew between the synchronous clock signal andthe skew calibration stream (block 806). In another embodiment of theinvention, a measure skew operation can be commanded by writing to anappropriate control register.

A skew measurement result is then transmitted from the preamplifiercircuitry 130 to the synchronous serial port control circuitry 112 overthe bidirectional serial data line 202-1, wherein the skew measurementresult is transmitted synchronously with the synchronous clock signal(PCLOCK) operating at the first frequency (block 808). The synchronousserial port control circuitry 112 uses the skew measurement result toalign the synchronous clock signal (PCLOCK) to digital signals (PDATA)to be transmitted over the bidirectional serial data line 202-1 (block810). For example, in one embodiment of the invention, the port logiccircuitry 216 uses the skew measurement result to access a correspondingdelay value that is stored in a local register, and use that delay valueto programmatically adjust the alignment circuitry 220 to adjust a delayvalue of a delay line, for example, and adjust a phase of the PCLOCKsignal. In particular, the alignment circuitry 220 will apply a delay tothe clock signal PCLOCK output from the clock generator 218 so as tophase align clock pulses of the synchronous clock signal (PCLOCK) toserially transmitted data bits of the digital data stream (PDATA)transmitted over the bidirectional serial data line 202-1. Followingalignment, a frequency of the synchronous clock signal (PCLOCK) isincreased from the first frequency to a second frequency, which isgreater than the first frequency (block 812). In one embodiment of theinvention, the second frequency is the normal operating frequency of thesynchronous serial data port (e.g., 1-2 GHz).

In the skew measurement process of FIG. 8, after reset of thepreamplifier circuitry 130, the PCLOCK signal stream and PDATA datastream are temporarily operated at a lower frequency (e.g., 100 MHZ)than the normal operation frequency (e.g., 1-2 GHz) of the synchronousserial data port. This enables the measure skew control character, whichis transmitted over the bidirectional serial data line 202-1 to initiatethe skew measurement process, to be reliably detected by thepreamplifier circuitry 130 despite any minimal time skew. Indeed, suchminimal time skew would not degrade the ability to properly detect theserially transmitted data bits of the skew measure control characterthat are synchronously transmitted at the lower PCLOCK frequency.Moreover, while the actual skew measurement between the skew calibrationstream and PCLOCK signal stream can be implemented at the slowerfrequency or the higher operating frequency of the serial data port, itis preferable that the skew result is transmitted back to thesynchronous serial port control circuitry 112 with the PCLOCK operatingat the lower frequency. This enables the skew result to be reliablydetected by the synchronous serial port control circuitry 112 despiteany minimal time skew, because such time skew would not degrade theability to detect the serially transmitted data bits of the skew result,which are synchronously transmitted at the lower PCLOCK frequency.

FIG. 9 is a block diagram of skew measurement circuitry according to anembodiment of the invention. In particular, FIG. 9 illustrates skewmeasurement circuitry 900 that is implemented in the preamplifiercircuitry 130 to perform a skew measurement process as described abovewith reference to FIG. 8, according to an embodiment of the invention.Moreover, FIG. 10 is a timing diagram that illustrates a method ofoperation of the skew measurement circuitry 900 of FIG. 9 to generate askew measurement result which is used to align a synchronous clocksignal with digital signals to be transmitted over a bidirectionalserial data line, according to an embodiment of the invention.

As shown in FIG. 9, the skew measurement circuitry 900 comprisesserial-in-parallel-out (SIPO) circuitry 912, decoder circuitry 914, afirst SR flip-flop 916, a second SR flip-flop 918, counter and decodingcircuitry 920, switching circuitry 922, encoder circuitry 926, andparallel-in-serial-out (PISO) circuitry 926. The skew measurementcircuitry 900 also includes the phase detector circuitry 230 shown inFIGS. 2 and 3. As depicted in FIG. 9, the sequencing operations of thevarious circuit components 912, 914, 916, 918, 920, 924, 926, and 230 ofthe skew measurement circuitry 900 are synchronously controlled by arising edge of the synchronous clock signal PCLOCK which is input to theclock port of each of said components.

In one embodiment of the invention, the various circuit components 912,914, 916, 918, 920, 922, 924, and 926 of the skew measurement circuitry900 are components of the port logic circuitry 226 (slave) shown inFIGS. 2 and 3, which are used in conjunction with the phase detectorcircuitry 230 to implement the skew measurement circuitry 900. Inparticular, the SIPO circuitry 912, decoder circuitry 914, counter anddecoding circuitry 920, encoder circuitry 924, and the PISO circuitry926 are circuit components that are employed by the port logic circuitry226 (slave) during normal transactions of the synchronous serial port.The first and second SR flip-flop circuits 916 and 918 and the phasedetector circuitry 230 are utilized in conjunction with the circuitcomponents 912, 914, 920, 924, and 926, for example, to perform a skewmeasurement process.

In general, the SIPO circuitry 912 receives a serial data stream (PDATA)that is transmitted from the synchronous serial port control circuitry112 over the bidirectional serial data line 202-1 and converts theserial data into parallel data blocks (e.g., bytes) using knowntechniques. The parallel data blocks (output from the SIPO circuitry912) are input to the decoder circuitry 914, wherein the decodercircuitry 914 decodes the data blocks to recover data and controlcharacters that are transmitted to the preamplifier circuitry 130. Forexample, the data may be register data that is to be stored inassociated register banks of the preamplifier circuitry 130, where theregister data is used to execute or otherwise support various functionsof the preamplifier circuitry 130. Moreover, the control characters mayinclude predetermined characters that instruct the preamplifiercircuitry 130 to perform various functions.

For example, in the context of skew measurement, the decoder circuitry914 will identify a predefined control character (Measure_Skew controlcharacter) that is transmitted to the preamplifier circuitry 130 tocommence a skew measurement process as described above with reference toFIG. 8. In one embodiment of the invention, where serial data istransmitted over the bidirectional serial data line 202-1 using 8 b/10 bencoding, the decoder circuitry 914 implements methods for decoding the8 b/10 b data blocks, and the encoder circuitry 924 implements methodsfor generating 8 b/10 b encoded data blocks for transmission over thebidirectional serial data line 202-1 to the synchronous serial portcontrol circuitry 112.

When the decoder circuitry 914 detects a predefined 8 b/10 b controlcharacter that is assigned to initiate a skew measurement process, thedecoder circuitry 914 will output a control signal, Measure_Skew, to aset port (S) of the first and second SR flip-flop circuits 916 and 918,which serves to “set” the first and second SR flip-flop circuits 916 and918. More specifically, in one embodiment, in response to detecting askew measure control character, the decoder circuitry 914 will output apulse to “set” the first and second SR flip-flop circuits 916 and 916,resulting in a logic “1” level maintained at the output ports (Q) of thefirst and second SR flip flop circuits 916 and 918.

As shown in FIG. 9, the Q output of the first SR flip-flop circuit 916is connected to an Enable input port of the phase detector circuitry230. Further, the Q output of the second SR flip-flop circuit 918 isconnected to a control input of the counter and decoding circuitry 920and to a control input of the decoder circuitry 914. A “set” logic level(MEAS_SKEW set to logic “1”) at the Q output of the first SR flip-flopcircuit 916 serves to enable the phase detector circuitry 230 to begin aprocess for determining a phase difference (P) between the PCLOCK clocksignal and a skew calibration stream transmitted on the bidirectionalserial data line 202-1. In addition, a “set” logic level (BLANK_PORT setto logic “1”) at the Q output of the second SR flip-flop circuit 918causes the counter and decoding circuitry 920 to commence a countingprocess. This counting process counts a number of clock cycles of thesynchronous clock signal

PCLOCK, which are input to the clock port of the counter and decodingcircuitry 920 after the second SR flip-flop circuit 918 is set inresponse to the Measure_Skew control signal. Furthermore, a “set” logiclevel at the Q output of the second SR flip-flop circuit 918 causes thedecoder circuitry 914 to temporarily suspend a decoding process, asthere is no need to decode any PDATA transmitted on the bidirectionalserial data line 202-1 during a skew measurement process.

The phase detector circuitry 230 can be implemented using known circuitarchitectures and phase detection techniques. In general, the phasedetector circuitry 230 is configured to compare arriving edges of thePCLOCK signal and a skew calibration stream (e.g., calibration clocksignal) transmitted on the bidirectional serial data line 202-1 todetermine a phase difference between the PCLOCK signal and skewcalibration stream. For example, in one embodiment, the phase detectorcircuitry 230 can be implemented using a well-known architecture whichcomprises a digital phase detector and charge-pump, followed by ananalog to digital converter. In another embodiment, the phase detectorcircuitry 230 can be configured to make a direct digital measurementusing an inverter chain to freeze relative positions of the

PCLOCK and skew calibration signals. In yet another embodiment, phasedetection can be implemented using an approach that relies on BER (biterror rate) detection against a pseudo-random binary sequence (PRBS)locally generated in the preamplifier circuitry 130. Phase detectioncircuits and methods are well known in the art and, consequently, adetailed explanation is not needed for one of ordinary skill in the artto understand embodiments of the invention as discussed herein.

The counter and decoding circuitry 920 generates a first control pulseR1 to “reset” the first SR flip-flop circuit 916. In particular, aftercounting a first predetermined number of rising edges of the PCLOCKsignal (i.e., count value meets a first predetermined value), thecounter and decoding circuitry 920 generates and outputs the firstcontrol pulse R1, which is input to a reset port (R) of the first SRflip-flop circuit 916. The first control pulse R1 causes the Q output ofthe first SR flip-flop circuit 916 to transition to a logic “0” level.When the MEAS_SKEW control signal is at a logic “0” level, the phasedetector circuitry 230 terminates the phase detection process. At thistime, the phase detector circuitry 230 temporarily holds a determinedphase difference value (denoted as “P”) for a subsequent period of timethat it takes for the preamplifier circuitry 130 to gain control of thebidirectional serial data line 202-1 for transmitting the phasedifference value P as a “skew result” to the synchronous serial portcontrol circuitry 112.

Moreover, the counter and decoding circuitry 920 generates a secondcontrol pulse R2 to “reset” the second SR flip-flop circuit 918. Inparticular, after counting a second predetermined number of rising edgesof the PCLOCK signal (i.e., count value meets a second predeterminedvalue after the first predetermined value), the counter and decodingcircuitry 920 generates and outputs the second control pulse R2, whichis input to a reset port (R) of the second SR flip-flop circuit 918. Thesecond control pulse R2 causes the Q output of the second SR flip-flopcircuit 918 to transition to a logic “0” level. When the BLANK_PORTcontrol signal is at a logic “0” level, the counter and decodingcircuitry 920 generates a control signal to the phase detector circuitry230 to output the determined phase difference value P for encoding andtransmission of the encoded P value as a “skew result” to thesynchronous serial port control circuitry 112. In addition, when theBLANK_PORT control signal is at a logic “0” level, the decoder circuitry914 is enabled for decoding subsequent blocks of serial data that may bereceived over the bidirectional serial data line 202-1 following theskew measurement process.

The phase difference value P comprises a plurality of data bits (e.g.,byte) that are output in parallel from the phase detector circuitry 230and input to the encoder circuitry 924 through the switch 922. In oneembodiment, the encoder circuitry 924 8 b/10 b encodes the phasedifference value P into a “skew result” character. The skew resultcharacter is input to the PISO circuitry 926, wherein the data bits ofthe skew result character are serialized and transmitted over thebidirectional serial data line 202-1 to the to the synchronous serialport control circuitry 112. When a skew measurement process is not beingperformed, the switch 922 is configured to pass other preamplifierregister data (which is access from the register bank and command logiccircuitry 246, FIGS. 2, 3) for encoding, serialization, and transmissionover the bidirectional serial data line 202-1 of the digital bus 202 tothe synchronous serial port control circuitry 112.

In an alternate embodiment of the invention, except for the phasedetector circuitry 230, the functions of the various circuit componentsshown in FIG. 9 can also be performed under control of firmware executedin the hard disk controller 102 (FIG. 1) using the synchronous serialport in a manner as discussed herein, but operating at a throttled-downclock rate. In such embodiment, a writeable register bit would be usedto perform the operation of the first SR flip-flop circuit 916 asdiscussed above. Upon conclusion of a skew measurement, the port logiccircuitry 216 (master) would read the skew result from a holdingregister in one of the register banks 246 in the preamplifier circuitry130.

FIG. 10 is a timing diagram that illustrates a method of operation ofthe skew measurement circuitry of FIG. 9, according to an embodiment ofthe invention. In particular, FIG. 10 schematically illustrates a methodof operation of the skew measurement circuitry of FIG. 9 in conjunctionwith the method discussed above with reference to FIG. 8. In the contextof the embodiment of FIG. 9, for example, FIG. 10 illustrates an examplePCLOCK signal 1000 and PDATA stream 1020 which are transmitted on theclock signal line 202-2 and the bidirectional serial data line 202-1,respectively, to implement a skew measurement process according to anembodiment of the invention. Moreover, FIG. 10 depicts an exampleMEAS_SKEW control signal 1030 and BLANK_PORT control signal 1040, whichare output from the Q outputs of the first and second SR flip-flopcircuits 916 and 918 (FIG. 9) during a skew measurement process.

FIG. 10 depicts the PCLOCK signal 1000 at different periods of timebefore, during, and after, a skew measurement process. In particular,the different time periods of the PCLOCK signal 1000 as shown include areset period 1002, a slow clock period 1004, a fast clock period 1006, aslow clock period 1008, a clock-to-data alignment period 1010, and afast clock period 1012 (or normal operating period). As further depictedin FIG. 10, the PDATA stream 1020 comprises a plurality of data streams1022, 1024, 1026, and 1028, wherein the arrows in FIG. 10 denote atransmission direction of the data streams 1022, 1024, 1026, and 1028between the synchronous serial port control circuitry 112 and thepreamplifier circuitry 130.

As discussed above with reference to FIG. 8, to commence a skewmeasurement process, the preamplifier circuitry 130 is reset during thereset period 1002. In one embodiment of the invention, as shown in FIG.10, a reset of the preamplifier circuitry 130 is initiated by creating agap in the synchronous clock signal PCLOCK 1000, wherein no clock pulsesare transmitted on the clock signal line 202-2 for a predeterminedperiod of time. The gap in the synchronous clock signal PCLOCK 1000 isdetected by the gap detector circuit 228 (FIGS. 2 and 3) to signal areset of the preamplifier circuitry 130. In another embodiment of theinvention, as discussed in further detail below with reference to FIG.11, initiating a reset of the preamplifier circuitry 130 is performed bytemporarily increasing a common-mode voltage on the bidirectional serialdata line 202-1 or the clock signal line 202-2 of the digital bus 202. Apreamplifier reset is initiated each time a skew measurement process isto be performed. In one embodiment of the invention, a skew measurementprocess is automatically performed after a power-up of the preamplifiercircuitry 130. Moreover, a skew measurement process can be periodicallyperformed during run-time to re-measure skew and periodically adjust thePCLOCK/PDATA alignment to account for changes in skew that may occurover run-time dues to changes in operating conditions, e.g., changes intemperature, etc.

During the slow clock period 1004 following the reset period 1002, thePCLOCK signal 1000 is transmitted over the clock signal line 202-1 at afrequency (e.g., 100 MHz) which is less than a normal operatingfrequency (e.g., 1-2 GHz) of the synchronous serial data port.

Moreover, during the slow clock period 1004, the port logic circuitry216 (master) sends a Measure_Skew control character 1022 (e.g., 8 b/10 bcode) in the outbound PDATA stream to instruct the preamplifiercircuitry 130 to commence a skew measurement process to measure skewbetween the PCLOCK and PDATA streams. In this embodiment, theMeasure_Skew control character 1022 is transmitted synchronously withthe lower frequency PCLOCK signal 1000 during the slow clock period1004. This allows the SIPO circuitry 912 and decoder circuitry 914 (FIG.9) to reliability detect the serially transmitted data bits of theMeasure_Skew control character 1022 despite any minimal time skew,because such time skew would not degrade the ability to properly detectthe serially transmitted data bits of the Measure_Skew control characterthat are synchronously transmitted at the lower PCLOCK frequency.

At time tl during the slow clock period, it is assumed that theMeasure_Skew control character has been detected by the decodercircuitry 914, and that the decoder circuitry 914 has issued aMeasure_Skew control pulse to the set port (S) of the first and secondSR flip-flops 916 and 918, causing the Q outputs of the first and secondSR flip-flops 916 and 918 to transition to a logic “1” level. Indeed, asdepicted in FIG. 10, at time t1, the MEAS_SKEW signal 1030 (at the Qoutput of first SR flip-flop circuit 916) and the BLANK_PORT signal 1040at the Q output of the second SR flip-flop circuit 918) are depicted astransitioning to logic “1.” At time t1, the preamplifier circuitry 130switches to a skew measure mode.

At time t2, the fast clock period 1006 begins, wherein the PCLOCK signal1000 is transmitted over the clock signal line 202-2 at a frequency thatis greater than the frequency of the PCLOCK signal 1000 transmittedduring the previous slow clock period 1004. For example, in oneembodiment of the invention, during the fast clock period 1006, thefrequency of the PCLOCK signal 1000 is increased to a normal operatingfrequency of the synchronous serial data port (e.g., 1-2 GHz).Furthermore, at time t2, a change in the state of the PDATA streamoccurs, wherein the skew calibration stream 1024 begins to betransmitted on the bidirectional serial data line 202-1. In oneembodiment of the invention, the skew calibration stream 1024 is a clocksignal that is transmitted at the same frequency as the PCLOCK signal1000 is transmitted during the fast clock period 1006.

In the example embodiment of FIG. 10, it is assumed that PDATA changesstate on a falling clock edge of the PCLOCK signal 1000, and that therising edges of the PCLOCK signal 1000 are used to control the timing ofsequencing operations performed by the control logic that executes theskew measurement process. As such, as depicted in FIG. 10, the MEAS_SKEWcontrol signal 1030 and the BLANK_PORT control signal 1040 are assertedat the time tl of a rising edge of the last clock pulse of the PCLOCKsignal 1000 in the slow clock period 1004. Moreover, as shown in FIG.10, PDATA changes state by transmitting the skew calibration stream 1024at time t2 of a falling edge of the last clock pulse of the PCLOCKsignal 1000 in the slow clock period 1004.

During the fast clock period 1006, as noted above with reference to FIG.9, the MEAS_SKEW control signal 1030 is input to the Enable port of thephase detector circuitry 230 to commence a skew measurement processwherein the phase detector circuitry 230 is configured to measure therelative timing between the PCLOCK signal and the skew calibrationstream 1024 transmitted on the bidirectional serial data line 202-1. Ina conventional phase detector circuit, a voltage signal is generated(via a charge pump) which represents a phase different the PCLOCK signal1000 and the skew calibration steam 1024, which are input to the phasedetector circuitry 230. The phase detector circuitry 230 operates for apredetermined number of clock cycles of the PCLOCK signal 1000, which isdeemed, a priori, to be sufficient for the phase detector circuitry 230to complete a sequence of operations to detect a phase differencebetween the PCLOCK signal 1000 and the skew calibration stream 1024.

Moreover, during the fast clock period 1006, assertion of the BLANK_PORTcontrol signal 1040 serves to initiate a counting operation in thecounter and decoding circuitry 920 to count a number of clock cycles ofthe PCLOCK signal 1000 that are used to perform the skew measurementprocess of the phase detector circuitry 230. In addition, the BLANK_PORTcontrol signal 1040 serves to temporarily disable the decoder circuitry914 and essentially block communication (temporarily) between thesynchronous serial data port and other preamplifier circuitry 130 whichis not utilized for the skew measurement process.

Next, at time t3 as shown in FIG. 10, it is assumed that the counter anddecoding circuitry 920 has counted a first predetermined number ofrising edges of the PCLOCK signal 1000 (i.e., count value meets a firstpredetermined value) that was needed for the phase detector circuitry230 to complete a sequence of operations to detect a phase differencebetween the PCLOCK signal 1000 and the skew calibration stream 1024.Accordingly, at time t3, the MEAS_SKEW control signal 1030 transitionsto logic “0”, which causes the phase detector circuitry 230 to terminatethe phase detection process. As discussed above with reference to FIG.9, the MEAS_SKEW control signal is set to logic “0” by the counter anddecoding circuitry 920 outputting the first control pulse R1 to resetthe first SR flip-flop circuit 916 and generate a logic “0” at the Qoutput of the first SR flip-flop circuit 916.

For the remainder of the fast clock period 1006 from time t3 to time t4,the phase detector circuitry 230 can operate to digitize the detectedphase difference value (P) for output. For example, in a conventionalphase detector circuit where a voltage is generated (via a charge pump)which represents a phase difference between the PCLOCK signal 1000 andthe skew calibration stream 1024, the charge pump can be disabled attime t3, and the voltage that is maintained by the charge pump can bedigitized via and analog-to-digital converter to generate the digitalphase difference value (P).

At time t4, the slow clock period 1008 begins, wherein the PCLOCK signal1000 is throttled down to a lower frequency (e.g., 100 MHz) which is thesame or similar to the frequency of the PCLOCK signal 1000 in theprevious slow clock period 1004. During a period of time from t4 to t5,to avoid contention on the synchronous serial port, no PDATA istransmitted on the bidirectional serial data line 202-1. Rather, duringthe period from t4 to t5, the port logic circuitry 216 (master)relinquishes control of the bidirectional serial data line 202-1, andport logic circuitry 226 (slave) asserts control of the bidirectionalserial data line 202-1 by asserting the proper logic levels of thedirection control signals (+D/−D) to the respective multiplexingcircuitry 208/210, as discussed above. Furthermore, during the timeperiod from t4 to t5, the skew measurement is “frozen” wherein the phasedetector circuitry 230 maintains the skew measurement value (P) foroutput upon commend from the counter and decoding circuitry 920.

Next, at time t5 as shown in FIG. 10, it is assumed that the counter anddecoding circuitry 920 has counted a second predetermined number ofrising edges of the PCLOCK signal 1000 (i.e., count value meets thesecond predetermined value) needed to (i) digitize the skew measurementvalue and to (ii) switch control of the bidirectional serial data line202-1 to the preamplifier circuitry 130 to transmit the skew result tothe synchronous serial port control circuitry 112. Accordingly, at timet5, the BLANK_PORT control signal 1040 transitions to logic “0”, whichcauses the counter and decoding circuitry 920 to terminate the countingprocess, and which enables the decoder circuitry 914. As discussed abovewith reference to FIG. 9, the BLANK_PORT control signal 1040 is set tologic “0” by the counter and decoding circuitry 920 outputting thesecond control pulse R2 to reset the second SR flip-flop circuit 918 andgenerate a logic “0” at the Q output of the second SR flip-flop circuit918.

During the slow clock period 1008, when the BLANK_PORT control signal1040 is de-asserted, the phase detector circuitry 230 outputs (uponcommand from the counter and decoding circuitry 920) a plurality ofparallel bits representative of the digitized skew measurement value(P). The digital skew measurement value (P) is encoded and serialized bythe encoder circuitry 924 and the PISO circuitry 926, respectively, togenerate the skew result 1026 data stream that is serially transmittedto the synchronous serial port control circuitry 112 over thebidirectional serial data line 202-1. As shown in FIG. 10, the skewresult 1026 is serially transmitted synchronously with a lower frequencyPCLOCK signal 1000 during the slow clock period 1008. This enables theserially transmitted data bits of the skew result 1026 to be reliablydetected by the synchronous serial port control circuitry 112 despiteany minimal time skew, because such time skew would not degrade theability to detect the serially transmitted data bits of the skew result1026, which are synchronously transmitted at the lower PCLOCK frequency.

Next, during a period of time from t6 to t7 (i.e., the clock-to-dataalignment period 1010) following the slow clock period 1008, thesynchronous serial port control circuitry 112 uses the skew result 1026to align the PCLOCK signal to digital signals (PDATA) to be transmittedover the bidirectional serial data line 202-1 using techniques asdiscussed herein (e.g., using the alignment circuitry 220). Moreover, asdepicted in FIG. 10, during the clock-to-data alignment period 1010, noPCLOCK signal is transmitted on the clock signal line 202-2, and toavoid contention on the synchronous serial port, no PDATA is transmittedon the bidirectional serial data line 202-1. Rather, during such timeperiod from t6 to t7, while an alignment process is being performed bythe synchronous serial port control circuitry 112, the port logiccircuitry 226 (slave) can relinquish control of the bidirectional serialdata line 202-1, and the port logic circuitry 216 (master) can assertcontrol of the bidirectional serial data line 202-1 by asserting theproper logic levels of the direction control signals (+D/−D) to themultiplexing circuitry 208/210, as discussed above.

Following the clock-to-data alignment period 1010, the frequency of thePCLOCK signal 1000 is increased to a normal operating frequency of thesynchronous serial data port (e.g., 1-2 GHz). Accordingly, as shown inFIG. 10, during the fast clock period 1012 following the clock-to-dataalignment period 1010, the synchronous serial data port is operatednormally, wherein control/data blocks 1028 are transmitted between thesynchronous serial port control circuitry 112 and the preamplifiercircuitry 130 using techniques as described above with reference toFIGS. 5, 6 and 7, for example.

Since the recording channel circuitry 110 must read register data storedwithin the register banks 246 of the preamplifier circuitry 130, variousskew measurement and/or adjustment techniques can be implemented inaddition to, or in lieu of, the skew measurement protocol and circuitrydiscussed above with reference to FIGS. 8, 9 and 10. For example,depending on the frequency of operation, a self-clocking, 8 b/10 b linecoding protocol can be used to encode inbound serial port data from thepreamplifier circuitry 130 to the synchronous serial port controlcircuitry 112. This allows a full-speed inbound port operation whilemitigating the effects of skew.

In another embodiment, the frequency of the synchronous clock signalPCLOCK can be throttled down during inbound PDATA transfers from thepreamplifier circuitry 130 to the synchronous serial port controlcircuitry 112. This embodiment takes into consideration that the inboundPDATA transmissions are then not seriously affected by latency. Thisembodiment adds no complexity to the preamplifier circuitry 130.

As noted above, the ability to force an overriding reset of thepreamplifier circuitry 130 is useful in various instances, such as wheninitiating a skew measurement process. As discussed above, a reset ofthe preamplifier circuitry 130 can be performed by inserting a “gap”within the synchronous clock signal PCLOCK, which is detected by the gapdetector circuit 228 of the preamplifier circuitry 130 to trigger areset of the preamplifier circuitry 130. The reset gap should be apredefined minimum length of time which is at least longer than (i) theperiod of time of a half cycle of the PCLOCK frequency operating at thelowest data rate, (ii) the longest run length, and (iii) longer than theclock gap length that is used to trigger a mode turnaround (as discussedabove with reference to FIG. 7). The gap detector circuit 228 may beimplemented using an asynchronous timer which receives as input thePCLOCK signal and performs a counting process in the absence of PCLOCKpulses. Each time a rising edge of the PCLOCK pulse is received, theasynchronous timer is reset. When the asynchronous counter overflows(count threshold), it is assumed that the reset gap is detected.

In an alternative embodiment of the invention, a reset of thepreamplifier circuitry 130 can be triggered by changing a common-modevoltage of the PCLOCK and/or PDATA signals. For example, FIG. 11 is adiagram of a current mode logic (CML) implementation of a communicationlink 1100 with reset circuitry to force a reset of a preamplifier bychanging a common-mode voltage on a bidirectional serial data line or aclock signal line of a digital bus, according to an embodiment of theinvention. As shown in FIG. 11, the communication link 1100 comprises afirst differential amplifier 1110 and a second differential amplifier1120 coupled to opposite ends of a differential line (ZP, ZN). Thedifferential line (ZP, ZN) can be the bidirectional serial data line202-1 or the clock signal line 202-2 of the digital bus 202, asdiscussed above. The first and second differential amplifiers 1110 and1120 have a resistor-loaded CML amplifier topology, which drives acommon mode voltage onto the differential line (ZP, ZN) to enabledifferential signal communication over the differential line (ZP, ZN)between the synchronous serial port control circuitry 112 and thepreamplifier circuitry 130.

In particular, the first differential amplifier 1110 comprises adifferential input stage formed by differential transistor pair M0 andM1 and load resistors RO and Rl. The gates of transistors M0 and M1 aredifferential inputs that receive as input a differential voltage todrive a common mode voltage on the differential line (ZP, ZN). Thedrains of transistors MO and Ml are connected to the respective lines ZNand ZP of the differential line (ZP, ZN) to output a differentialvoltage (common mode voltage) on the differential line (ZP, ZN). Thefirst differential amplifier 1110 further comprises a controllable tailcurrent source Si that generates a bias current for DC biasing the firstdifferential amplifier 1110. Similarly, the second differentialamplifier 1120 comprises a differential input stage formed bydifferential transistor pair M10 and M11 and load resistors R10 and R11.The gates of transistors M10 and M11 are differential inputs thatreceive as input a differential voltage to drive a common mode voltageon the differential line (ZP, ZN). The drains of transistors M10 and M11are connected to the respective lines ZP and ZN of the differential line(ZP, ZN) to output a differential voltage (common mode voltage) on thedifferential line (ZP, ZN). The second differential amplifier 1120further comprises a controllable tail current source S2 that generates abias current for DC biasing the second differential amplifier 1120.

The communication link 1100 further comprises a common mode voltageadjustment circuit 1130 and a reset receiver 1140. The common modevoltage adjustment circuit 1130 comprises a first switch circuit 1132and associated tail current source S3, and a second switch circuit 1134and associated tail current source S4. In one embodiment of theinvention, the first and second switch circuits 1132 and 1134 aretransmission gates that are controlled by a reset control signal FORCERESET. When the preamplifier circuitry 130 needs to be reset, thecontroller temporarily asserts the FORCE RESET signal to activate (turnon) the switch circuits and connect the current sources S3 and S4 to thedifferential signal lines ZP and ZN, respectively. In response, thecommon mode voltage of the differential line (ZP, ZN) is temporarilychanged (e.g., decreased) due to the voltage drop generated across theload resistors R0 and R1 by virtue of the current sources S3 and S4being temporarily connected to the respective differential signal linesZP and ZN. The reset receiver 1140 detects this change in the commonmode voltage. The reset receiver 1140 outputs a reset control signal tothe preamplifier circuitry 130 to initiate a reset of the preamplifiercircuitry 130.

In other embodiments of the invention, multiple disk-based storagedevices 10 (FIG. 1) may be incorporated into a virtual storage system asillustrated in FIG. 12. In particular, FIG. 12 is a block diagram of avirtual storage system 1200 incorporating a plurality of disk-basedstorage devices of the type shown in FIG. 1. The virtual storage system1200, also referred to as a storage virtualization system,illustratively comprises a virtual storage controller 1210 coupled to aRAID system 1220, where RAID denotes Redundant Array of IndependentDisks. The RAID system 1220 more specifically comprises N distinctstorage devices denoted 10-1, 10-2, . . . , 10-N, one or more of whichare assumed to be configured to include embodiments of the storagedevice 10 as shown in FIG. 1 with multiplexed communication controlcircuitry as discussed herein. These and other virtual storage systemscomprising hard disk drives or other disk-based storage devices of thetype disclosed herein are considered embodiments of the invention. Ahost processing device may also be an element of a virtual storagesystem, and may incorporate the virtual storage controller 1210.

Although embodiments of the invention have been described herein withreference to the accompanying drawings, it is to be understood thatembodiments of the invention are not limited to the describedembodiments, and that various changes and modifications may be made byone skilled in the art resulting in other embodiments of the inventionwithin the scope of the following claims.

What is claimed is:
 1. A method to implement multiplexed communicationbetween a recording channel and a preamplifier in a storage device,comprising: switchably connecting a first input of read data circuitrywithin the recording channel to a first analog line of an analog bus toreceive first read data transmitted from the preamplifier to therecording channel over the first analog line during a read operation;and switchably connecting a write data output of write data circuitrywithin the recording channel to the first analog line to transmit writedata from the recording channel to the preamplifier over the firstanalog line during a write operation.
 2. The method of claim 1, furthercomprising: switchably connecting a second input of the read datacircuitry to a second analog line of the analog bus to receive secondread data transmitted from the preamplifier to the recording channelover the second analog line during the read operation; and switchablyconnecting a write control output of the write data circuitry to thesecond analog line to transmit a write control signal from the recordingchannel to the preamplifier over the second analog line during the writeoperation.
 3. The method of claim 2, wherein the write control signalcomprises a clock signal.
 4. The method of claim 3, wherein the clocksignal controls one of (i) a pattern dependent write operation and (ii)a heat-assisted magnetic recording operation.
 5. The method of claim 2,further comprising: switchably connecting a third input of the read datacircuitry to a third analog line of the analog bus to receive third readdata transmitted from the preamplifier to the recording channel over thethird analog line during the read operation; and switchably connecting awrite control input of the write data circuitry to the third analog lineto receive a write control signal transmitted from the preamplifier tothe recording channel over the third analog line during the writeoperation.
 6. The method of claim 5, wherein switchably connectingcomprises: controlling multiplexer circuitry of the recording channelduring the read operation to connect the first, second, and third analoglines of the analog bus to the first input, the second input and thethird input, respectively, of the read data circuitry; and controllingthe multiplexer circuitry of the recording channel during the writeoperation to connect the first, second, and third analog lines of theanalog bus to the write data output, the write control output, and thewrite control input, respectively, of the write data circuitry.
 7. Themethod of claim 5, wherein the first read data, the second read data,and the third read data are obtained by concurrently sensing data storedon the storage medium using a first read sensor, a second read sensor,and a third read sensor, respectively.
 8. The method of claim 5, whereinthe write control signal transmitted over the third analog line to thewrite control input of the write data circuitry comprises abit-patterned magnetic recording loopback control signal.
 9. The methodof claim 1, further comprising: controlling a bidirectional serial dataline of a digital bus to selectively transmit digital signals in eithera first direction from the controller to the preamplifier or a seconddirection from the preamplifier to the controller, in response to adirection control signal; and concurrently transmitting a synchronousclock signal over a clock signal line of the digital bus from thecontroller to the preamplifier to synchronize transfer and processing ofthe digital signals transmitted on the bidirectional serial data line ofthe digital bus.
 10. The method of claim 9, wherein the digital signalstransmitted in the first direction include register set-up data, andwrite mode and read mode control signals, and wherein the digitalsignals transmitted in the second direction include register readresults, and fault polling results.
 11. The method of claim 9, whereinthe direction control signal comprises a direction control characterthat is inserted in a digital signal stream transmitted in the firstdirection to signal a direction switch for transmitting digital signalsin the second direction.
 12. The method of claim 9, wherein thedirection control signal comprises a gap that is created in thesynchronous clock signal by the controller and transmitted over theclock signal line of the digital bus, wherein the gap in the synchronousclock signal is detected by the preamplifier to signal a directionswitch for transmitting digital signals in the second direction.
 13. Astorage device, comprising: a storage medium; a read/write headcomprising a read sensor and a write element; preamplifier circuitry,electrically connected to the read/write head, wherein the preamplifiercircuitry comprises read circuitry and write circuitry, wherein the readcircuitry is configured to drive the read sensor to read data from thestorage medium and to process the read data, and wherein the writecircuitry is configured to drive the write element to write data to thestorage medium; recording channel circuitry comprising read datacircuitry and write data circuitry, wherein the read data circuitry isconfigured to decode read data that is received from the preamplifiercircuitry, and wherein the write data circuitry is configured to encodewrite data that is to be written to the storage medium; an analog buscomprising a plurality of analog lines connecting the recording channelcircuitry to the preamplifier circuitry; and multiplexing circuitryconfigured to control transmission of read and write information signalsbetween the recording channel circuitry and the preamplifier circuitryover one or more of the plurality of analog lines, wherein the analogbus includes a first analog line, and wherein the multiplexing circuitryis configured to selectively transmit one of (i) write data over thefirst analog line from the recording channel circuitry to thepreamplifier circuitry during a write operation, and (ii) first readdata over the first analog line from the preamplifier circuitry to therecording channel circuitry during a read operation.
 14. The storagedevice of claim 13, wherein the analog bus includes a second analogline, and wherein the multiplexing circuitry is configured toselectively transmit one of (i) a write control signal over the secondanalog line from the recording channel circuitry to the preamplifiercircuitry during the write operation, and (ii) second read data over thesecond analog line from the preamplifier circuitry to the recordingchannel circuitry during the read operation.
 15. The storage device ofclaim 14, wherein the write control signal comprises a clock signal thatcontrols one of (i) a pattern dependent write operation performed by thewrite circuitry of the preamplifier circuitry and (ii) a heat-assistedmagnetic recording operation performed by heat-assisted magneticrecording circuitry included in the preamplifier circuitry.
 16. Thestorage device of claim 13, wherein the analog bus includes a thirdanalog line, and wherein the multiplexing circuitry is configured toselectively transmit one of (i) a write control signal over the thirdanalog line from the preamplifier circuitry to the recording channelcircuitry during the write operation, and (ii) third read data over thethird analog line from the preamplifier circuitry to the recordingchannel circuitry during the read operation.
 17. The storage device ofclaim 13, further comprising: serial port control circuitry; and adigital bus consisting of a bidirectional serial data line and a clocksignal line, wherein the multiplexer circuit is further configured toselectively transmit one of (i) digital signals in a first directionfrom the serial port control circuitry to the preamplifier circuitry and(ii) digital signals in a second direction from the preamplifiercircuitry to the serial port control circuitry, in response to adirection control signal; and wherein the serial port control circuitryis configured to generate and concurrently transmit a synchronous clocksignal over the clock signal line of the digital bus from the serialport control circuitry to the preamplifier circuitry to synchronizetransfer and processing of digital signals transmitted on thebidirectional serial data line.
 18. The storage device of claim 17,wherein the direction control signal comprises a direction controlcharacter that is inserted in a digital data stream transmitted in thefirst direction to signal a direction switch for transmitting digitalsignals in the second direction.
 19. The storage device of claim 17,wherein the direction control signal comprises a gap that is created inthe synchronous clock signal transmitted over the clock signal line ofthe digital bus, wherein the preamplifier circuitry comprises a gapdetection circuit configured to detect the gap in the synchronous clocksignal and generate a gap detection signal to initiate a directionswitch for transmitting digital signals in the second direction.
 20. Avirtual storage system comprising the storage device of claim 13.